Steve and Karen
Ranger
I, and another frequent forum contributor (Seth), have noted that there is not one independent thread that we can turn to for all the basic and semi-advanced information about the trailer battery, to allow us to get the most out of it, extend its life and guide us to its inevitable replacement. CI's manual can only practically touch on some of the battery's many aspects, which could rightly justify its own manual of operations. And as eager to help as Cary and Craig are with phone calls, emails etc, we can't can't be bugging them all the time. And it only makes sense to have a passable working knowledge of what is the heart of the trailer's capabilities.
Consequently, we have to search through this forum and other sites for how-to's and what's-its, and Q's & A's. Unfortunately, the information is greatly spread about the forum in multiple threads and is difficult to understand without reading the entire thread, as the various thread contributors work through various problems, solutions, back-and-forths, and their own personal learning curves. I thought I'd bring a lot of this generally agreed-upon information together in one place. For better, and (hopefully) not worse.
As a further justification of this lengthy tome, in a related post, Seth makes a number of good points about the need for CI owners to be Battery Literate, for lack of a better term:
Where it gets a little trickier is that batteries, unlike almost anything else on the trailer, can be easily damaged, do have a limited service life, and a replacement can’t be economically/safely shipped from Necedah. Batteries are hazardous materials as shipped; they go by truck freight. And some of us bought pre-owned trailers (no orientation, maybe no manual)... there is no national dealership or service network... etc.
Those who can do swing by Wisconsin for service! Those who can do so learn from this site and other research. Others have hit & miss experience with finding good RV service locally. Good shops do exist. Batteries are trickier...
Disclaimer: I am not an electrical engineer, and knew very little about batteries in general, before I owned the CI. But after fixing a shorted wire, adding solar, a third brake light and a spare lithium portable, I know a little more about the trailer's electrics, and the battery in general. I'll try to reference and provide links and more authoritative sources. But anything you see here should be cross-checked for your purposes and peace of mind, before you follow through on any purchase or modification. There will be differences of opinion. But certainly I am open to being corrected on factual errors. Amongst us there will also be differences in OEM battery/compartment specs, so please take those into account as well. If you're short on time, you can also scroll to the end for a summary.
I'm also not going to recommend specific batteries or sources for replacement, since what worked for one person may not fit, or work, for another. Also... learning that one person got 8 years out of a particular battery is a great starting point. Replicating that feat 8 years later with the "same" product whose quality control may have lapsed within that time isn't a sure thing. The corollary to this is that a poorly performing battery may not be the battery's fault, since there's lots of ways you can unknowingly mess up a battery. Which is part of the point of this thread.
Sticking with a reputable manufacturer with a good overall track record, and judiciously matching up the specs of their current batteries with your own, is likely the safest route. Consulting with CI as to their current battery of choice will also likely serve you well. Since CI will have undoubtedly done their due diligence in this area.
OEM Battery Size and Compartment
For a long while CI has elected to go with a Group 24 size battery, although in the beginning they apparently used a 12V that was physically smaller than the current one. See Cary's clarification: Battery - Bigger Battery Although the currently used Group 24 is an industry standard size, not all manufacturers' batteries are exactly identical. Post type, position and orientation can be slightly different and make it problematic, and sometimes impossible, to install. Because the battery compartment is designed like the rest of the TD... i.e no wasted space... any prudent replacement should involve a careful measurement of what came out of your trailer (regardless of what I have written above), and to not try to exceed it with a larger battery, unless there's actual room to do so. Replacement with a battery whose terminal positions or design don't match what is already in there, or with a battery whose case is not a perfect rectangular box shape, can also be problematic . Modifications to the compartment to make things fit, aren't easy, fun or (possibly) pretty.
OEM Battery Types and Specs
This will vary slightly between owners and trailer manufacture dates. New owners of old CI trailers may not know what originally came with their trailer, or if what is in there now matches the original size and specs. My 2017 came with an Everstart Group 24DC "Marine" sealed flooded lead-acid "Deep Cycle" battery with 690 Marine Cranking Amps; CI had been putting this size into the trailer some time before that, and has continued to do so since. If not, then with an near identical facsimile. For about $100 more, CI continues to offer the option of an AGM battery upgrade, which is exactly the same physical size. AGMs are also lead acid, but are constructed differently, and mitigate some of the problems of misuse or abuse. (More about that later.) Their main selling feature is that for about an additional one half the cost of a new flooded battery, you can get twice the life expectancy: "AGM batteries typically have about twice the lifespan of our standard Deep Cycle (flooded) lead-acid batteries. The major factor determining long-life for any lead-acid battery is keeping the battery charged when it is in storage or during periods of non-use." (from the CI store page) .
Regardless of their AGM or flooded construction, OEM Group 24 lead-acid batteries are limited by basic physics to a rating of about 75 Amp/Hours. A/hrs are a rough measure of its overall capacity, and are akin to Watt/ Hours, which is another commonly used metric. W/hrs when divided by 12 = Amp/hours, when you a dealing specifically with a 12V electrical system. Larger Group 27 and Group 31 batteries offer tantalizingly bigger outputs, but they won't fit any stock CI trailer. A 75 A/hr battery will get the average user through about 3 days of dry camping using the lights, water pump, and fan, before it needs recharging. YMMV, of course.
Also, don't take other Group 24 manufacturer-stated A/hrs or W/hrs as gospel. There's different ways to measure that and many go for the one that looks and reads best. Make sure they are quoting the "20 Hour Rate", which is usually reserved for testing and rating Deep Cycle batteries, so you can compare apples to apples. The 100 hour rate is always higher, and would be misleading.
CI likely ended up on the current Group 24 sizing and A/hr capacity as both specs fit in well with their design, the overall economics, ergonomics, ease of future replacement, and the user needs of the vast majority of trailer buyers. Some forum members (including myself) for various personal reasons and needs, have opted to increase this respectable capacity in various ways, through the use of larger batteries, additional batteries, on-board battery systems with a different chemistry (lithium), solar systems and generators. Though frequently successful, sometimes this is achieved at considerable expense, effort, and occasionally, regret.
What is a Deep Cycle Battery?
(Here's what started my quest for the appropriate Deep Cycle battery replacement, and was ultimately the most confusing aspect of the hunt, for me.)
Basically, standard car batteries have more and thinner plates for the acid to work on. Resulting in a greater surface area and capacity to produce amperage. Which is what you need for turning over an engine: a short powerful electrical burst. It's a cheetah and will run out of steam in short order. Deep Cycle them and they will die. Not the best type of battery for a trailer, whose amperage demands are much lower and spread out over more than 4 seconds of cranking. Generally speaking, "Deep Cycle" batteries have fewer and thicker plates than auto batteries. You can draw more electricity from it, and over a longer time, before you start to change the internal chemistry and/or cause damage. Deep Cycle batteries are better for RVs and trailers. That's the basics.
Unfortunately, the term "Deep Cycle" gets thrown around. A lot. Most batteries that are held out to be Deep Cycle are actually a hybrid design, and are really meant for marine applications: they have to start a motor (i.e. have cranking capacity like a car battery) but also have to power things for a long time all on their own, like lights and trolling motors, when the main motor isn't producing electricity through the alternator and recharging the battery. Unlike car batteries, Deep Cycle/ Marine batteries can be taken down to about 50% Depth of Discharge (more later) before they have to be recharged. Perfect for marine applications. Nearly perfect for trailering, since we don't necessarily need the cranking capacity. But the cranking is there for us nonetheless. Especially if the Tow Vehicle needs a boost and you're in the middle of nowhere. However, a Marine battery is a hybrid, and as such, a compromise: pretty good at most things, an expert at nothing. Bottom line: if the battery or its literature states cranking amp specs in the area of 550 to 700, then it is a hybrid and likely will perform as a hybrid, and not a true Deep Cycle.
The RV and trailering community has had little choice but to rely upon the marine market for their trailer batteries. There are very few RV-dedicated batteries out there. However, marine batteries are easy to find and they generally don't cost an arm and a leg. But because they are ubiquitous, and are sold by many retailers whose main customer base is not specifically tiny trailers (i.e. automotive, hardware, solar, marine supply), they can also vary greatly in quality. So doing your homework is necessary.
A true Deep Cycle battery, on the other hand, has little cranking ability, but can be taken down even further than the 50% DOD on a regular basis, sometimes down to 20% or even 0% without damage. These are almost entirely designed and meant for the solar/wind/ industrial stationary market. Their sizes, shapes and oddball voltages, like 2V, 6V, 8V, make them generally unsuitable as a replacement in the current CI. There are however a couple exceptions; (more later). In truth, a true Deep Cycle battery for our trailer is exactly what it could use, to provide the greatest utility, speaking solely from an electrical standpoint. But because a true Deep Cycle battery is meant for stationary applications, its standard internal construction may not be robust enough to withstand the rigors of being jostled at the rear of the trailer, where vibrations and bumps are amplified. Even if it did fit the space, and even if it was the proper voltage.
What is Depth of Discharge?
It seems counterintuitive that a 12V battery that registers 11.0V could be "dead" and not provide any power to anything. But it is, and it may not come back to life either, or its original condition, even if you think that you have successfully recharged it. A fully charged 12V battery at 100% should read 12.7V to 12.8V. Immediately after charging it may even read higher than this before it "settles down". During charging, it will even read, and should read, in the mid-13's and slightly into the 14's. A 12V lead acid battery (Marine, hybrid or designated Deep Cycle) can be taken down to 50% of its capacity without doing any damage; this corresponds with a voltmeter reading of about 12.1 volts. Go below this Depth of Discharge (DOD) reading at your peril. I've attached at the end of the post a photo of a chart that I use for reference, and have taped to the right bin lid cover so I won't be wondering about how much juice I have left to play with.
To be fair, a voltmeter reading of an actively used battery is only a guesstimate of the State of Charge/ Depth of Discharge. The SOC is affected by ambient temperature and how recently the battery has been used. However, temperatures colder than 70 degrees actually provide you with a bit of a safety buffer, if you stick to the 12.1 cut-off. For accurate results, take the reading with no devices draining the battery. Better yet, wait an hour. Or take it in the morning after no battery usage for even greater accuracy.
Generally, no lead acid battery, whether flooded or AGM, should be taken below 50%. Seth, however, has located two batteries: Victron Super Cycle (not all their AGM) and some C&D Dynasty UPS batteries, whose literature suggests an occasional deeper discharge is not fatal, but is not really recommended either if you want to squeeze a maximum life out of it. These batteries are definitely the exception, and not the rule, when it comes to a Deep Cycle lead-acid safe DOD. Some Rolls and Concorde batteries may also be in that category.
The flip-side of the deep discharge is that repeated shallow discharges (less than 10%) can also be damaging and negatively affect service life. So it is a good idea to take the battery out for a "run" every once in a while, especially if your camping style is always established campgrounds with electrical service.
It should also be noted that a 50% DOD limitation also corresponds with a battery that can now only perform half of its stated A/hr rating. If you have added up all the amp draws of all your devices, and calculated your A/hr needs to be 100, for example, you will require a 200 A/hr battery to get all the work done. Correspondingly, our 75 A/hr trailer lead acid battery can only give us 32 A/hrs of work before it needs to be recharged, or before we do damage to it. This could impact your decision as to whether or not a single Group 24 battery is sufficient for your needs.
When assessing your battery's condition, a TriMetric Battery Monitor can also help you figure out what's going on with it, in certain areas that a simple voltmeter can't: Teardrop Travel Trailers by Camp-Inn , Trimetric - on a galley door?? , Best Battery Monitors for RV's, boats,off-grid cabins, vanlife
Leaving your 7-pin connected to the TV while parked or camping, and using your trailer's 12V system, can present a problem for your TV's battery depth of charge. There will be a drain on your TV battery, which is far less tolerant of deep discharges. You'll be taking both batteries down simultaneously, and your TV battery may not have enough juice to start the TV. A battery isolator, either installed on the TV, or the trailer will prevent this in the event you forget to disconnect. Teardrop Travel Trailers by Camp-Inn , Isolator - Battery Isolator
As far as what to do between trips? Leave the trailer plugged in and charging and it will be happier. Any lead acid battery will have a natural discharge rate, even if disconnected from the trailer wiring. Leave the main switch "on", and not charging, and there will be an even further "phantom draw" on the battery. Subject to other and plentiful variables, including age and temperature, a battery could easily self-discharge to the point of damage after only a couple months of not being plugged in to the wall: Battery Care Between Trips. As Cary states, leaving it plugged in also verifies the proper functioning of the charger at any time, with a peek.
There's lots of data out there about DOD compared to the number of full cycles in a battery's lifetime, and getting the most total A/hrs out of your battery, blah blah... A good basic rule is to simply stay as far away from the 50% as best you can, topping up completely whenever you can, and occasionally letting the battery actually do some work. And your battery and wallet will thank you.
What is the Difference Between a Standard Flooded and an AGM Deep Cycle?
In addition to the cost-vs-life-expectancy differences/advantages I touched on above (you'll have to do your own math on that, and with what is available in your area, on sale, or through a CI install, etc...) there are some other differences between the two batteries where some may find an AGM to be to their benefit:
1) AGMs are far less prone to leakage and spillage.
2) Because of their construction, they are even more robust than other Deep Cycle /Marine/ RV flooded batteries and more resistant to the jostles of the road.
3) An AGM may also be more tolerant of partial discharging, followed by a partial recharge.
In a partial recharge (less than 100%), followed by a discharge, a standard flooded lead acid battery can be prone to acid "stratification", which (to be very brief and non-technical) isn't a good thing for the life expectancy of the battery. When connected to the campsite post, it's not difficult to get a 100% uninterrupted recharge. On the road this can be a different matter, depending upon the abilities of your TV alternator. Many new 'smart' TV alternators can only take the trailer battery back up to 85% while on the road. See this about the CTEK device as a solution for this problem: Teardrop Travel Trailers by Camp-Inn and any other CTEK-related posts. Essentially, a CTEK will regulate and optimize recharging from multiple and simultaneous sources (TV, solar) to achieve a 100% battery recharge.
Uninterrupted charging all the way to 100%, by way of solar alone, can also be difficult to achieve, for reasons of cloud, shade or lack of sunlight. So stratification can be a risk with independent solar systems, and flooded batteries.
I really don't want sway anyone one way or the other, but AGMs certainly seem to have the upper hand. Particularly if you factor in the consideration of fewer replacements, and less environmental waste, since with care they can last twice as long.
If you do go with flooded lead acid battery replacement, make sure that it "sealed". That is to say that it requires no upkeep (water top-up) or venting, which would be evident by a series of removable caps. The battery compartment is too confined to support a vented battery and would collect the gases, which would be dangerous. AGMs by their design are sealed, which will always negate this concern. A sealed flooded lead acid battery is sometimes marketed as a VRLA (valve-regulated lead acid) but it is the same thing.
Get a battery that 'just fits'. Too small a battery will deprive you of amp hours as well as possibly cause damge to itself or the compartment by bouncing around. (Replacement battery - where to buy?)
I've Already Tried Camping and I Want 12V Power For longer Than The OEM Battery Can Provide; What Do I Do?
Between the 75 A/hr battery, 100% road charges in between destinations, and the occasional/frequent use of electrical sites, most of us will have the capacity to stay above 50% DOD almost all the time. But sometimes some of us just need more. Some like to get away from everyone, and boondock, for a long time. Others want to run a lot of hungry devices, or power a fridge in hot weather. Some absolutely need supplemental and reliable power for things like a CPAP. The trailer battery alone will either be severely challenged, all the way to grossly inadequate, under some of these conditions.
Each of these following mods/add-ons that are designed to provide more power to your rig, has its benefits, costs and disadvantages. But you could:
1) Install a Lithium Battery, that can be cycled below 50%. This comes with a complete re-think of the trailer's capacities, including a replacement of the OEM charge controller. As well as extra cost. But it can be done. Several forum members have travelled this adventurous road and enjoyed the journey: Good Discussion Of Lithium Batteries , Battery - Agm Vs Lithium. and Lithium Battery Charger
2) Carry a spare battery. This is an additional Group 24 battery that you can travel with fully charged in the TV, and replace with the OEM in the compartment when necessary. It's heavy. And safe, convenient transport can be a challenge. As well, there is the cumbersome act of switching out 50 lb lumps. Alternatively, you can connect it via one of the trailer's 12V sockets, without installing it in the compartment. Provided you disconnect the main battery first. An adequate gauge 12V to 12V 15A protected connection is required.
3) Carry a portable lithium battery station, like a Goal Zero. This much lighter option (than comparably sized lead-acid) requires no additional trailer wiring or devices and can plug directly into the trailer's 12V sockets (as above) with the proper connections and the mandatory main battery disconnect. It can power or recharge other devices, like fridges, well away from the trailer. Or elsewhere. Good feedback of usage and capacities through LED displays, with multiple recharging options. Can be costly, if you go with a quality unit: Good Discussion Of Lithium Batteries
4) Install a solar panel, either portable, or mounted or hardwired. (lots of good info and experience on the forum with equally intriguing and variable configurations)
5) Connect a gas generator. To either power or recharge your 12V devices or recharge the trailer battery through the 120V rear plug. This will also give you some 120V service separate from the trailer, depending on the size of the unit and your inverter.
6) Operate the Tow Vehicle for a short period to recharge the trailer battery.
7) Install a second battery in the trailer in parallel. Very few will try to convince you that this is a good idea. If it was, it would be a CI ordering option for those who want or need more capacity; it isn't. There is little room for such a modification, and for a variety of technical reasons CI has many times advised against it: Battery - Bigger Battery , Adding A Second Battery
8) Install a single larger battery to get more A/hrs, taking on the necessary 'challenging' modifications to the battery compartment: New Td Battery On Its Way. Read Seth's caveat about his project in this: Battery - Agm Vs Lithium
9) Install, or carry, a 'Pony Battery'. This is an auxiliary sealed lead-acid battery, which can be of any size, not just a Group 24. It can supply supplemental power to any device, like a fridge or CPAP, directly, provided that you understand what is going on with it's rate and depth of discharge. Unlike options 7 and 8 which are hard-wired into the trailer's existing system, charge controller and meter, a pony's wiring (if any) is distinct from the trailer's wiring. However, it can be used to power all the trailer's lights, pump and fan through a 12V socket... much like the options 2 and 3. Again, when doing so, it is crucial to disconnect the main trailer battery, or risk disparate simultaneous draw-downs, back-feeding and blown fuses (Thanks for those corrections, Seth) Cpap Power For Boondocking
With Options 2 and 9, you now have to come up with a recharging solution, for your depleted supplemental lead-acid, or resign yourself to carrying around useless weight for the remainder of the trip. Not an insurmountable task by any stretch. There are solar solutions, and some members (I believe) have modified their tow vehicles with additional on-board battery charging, though you want to make sure that your TV alternator is up to the task: Auxiliary Battery For Refrigerator Adding another 120V charger dedicated to the pony is also an option. But this is where Option 3, that has its own on-board charge controller, and which can be recharged from multiple sources (TV 12V, solar, 120V), has a distinct advantage.
I Didn't Really Want To Read Everything Up To This Point. What Are The Take-Aways?
I've undoubtedly missed some things, but I believe the following to be good and true advice:
1) Carefully measure your space and old battery before buying a new one. Look at the terminals/posts, their placement, and type. There's lots of different configurations. Most Group 24s will work, if that's what you had before. But measure anyway. Take into account the posts when reading the manufacturer's measurements. Too small a battery is also not good, as it will short-change you on A/hrs as well possibly cause damage to itself or the trailer if not secured.
2) Consider an AGM, either with your CI order, or aftermarket as a replacement. Properly cared for it should provide better service, utility, on a number of different levels. And better long-term economy. If you're really bad at looking after things, then maybe a more expensive pet like an AGM isn't the best idea.
3) You will likely end up with another Marine Deep Cycle battery as a replacement when the time comes. Make sure it is a quality one so that it in fact can handle the Deep Cycle part of the equation. The better it is at cranking, the worse it will be at the other.
4) If you want one that will do better than a standard Marine battery, and are jonesing for a true deep cycle battery that fits the battery space and can go below 50% DOD, really do your physics homework, study the spec sheets, and crunch the economics numbers as well.
5) If you have anything other than a lithium battery, which will be almost all of us, don't go below 50% DOD, or 12.1V. If your trailer doesn't have a battery monitor, or voltmeter in the right hand bin, get one. Or learn how to use a hand-held meter with the battery terminals or the 12V sockets. One or two deep unintentional discharges and you could be be several hundred dollars to the poorer. Or in the dark.
5.1) Keep your trailer plugged in and battery charging between trips. However, an always full battery isn't always good either. Occasionally let your battery naturally discharge more than 10% (or actually go out and use it!) to prevent damage and prolong its life. When camping, remember to always disconnect from your TV, unless you have a battery isolator. Then don't worry.
6) If you have a flooded lead acid (not AGM) and a newer vehicle, consider a CTEK as a way to get full charging on the road, and guard against stratification damage caused by partial charging. Consider it, even if you have an AGM, just so you are always topped up to 100% after coming off the road.
7) If you can, get as many trips in under varying travel conditions, to determine your electrical needs before you pull the trigger on something different than the OEM battery. Monitor your battery draw-down (how close you come to 12.1V) and/or calculate your projected A/hrs required with all your devices and on-board power draws. You might be surprised at how little you actually use, and that the OEM type of battery is more than adequate for most of your needs, most of the time.
8) Rather than attempt an oddball battery replacement to improve upon the trailer battery's capacity, consider one of the many other add-on solutions. Many of us who have attempted supplemental power are more than happy to advise what went well, and what went sideways, with our various projects/obsessions, and how to pull them off, so that you have all the power you need, or think you need. And then some.
In addition to the forum, CI's site, and other members' valuable and knowledgeable contributions and experience through the years, I also drew from the manufacturer's sites of high-quality batteries (like Trojan, Concorde and Rolls), and these more generic sources, among others:
Replacement battery - where to buy?
Basic to Advanced Battery Information from Battery University
Water Loss, Acid Stratification and Surface Charge - Battery University
Learning Center | Northern Arizona Wind & Sun
If I am off-base with anything or have misinterpreted information, please let me know and I'll "unsend" and correct the text. That way no one has to scroll any further to find the right info.
Thanks,
Steve
(If I've saved only one battery from an early death... it will have been worth it.)
Consequently, we have to search through this forum and other sites for how-to's and what's-its, and Q's & A's. Unfortunately, the information is greatly spread about the forum in multiple threads and is difficult to understand without reading the entire thread, as the various thread contributors work through various problems, solutions, back-and-forths, and their own personal learning curves. I thought I'd bring a lot of this generally agreed-upon information together in one place. For better, and (hopefully) not worse.
As a further justification of this lengthy tome, in a related post, Seth makes a number of good points about the need for CI owners to be Battery Literate, for lack of a better term:
Where it gets a little trickier is that batteries, unlike almost anything else on the trailer, can be easily damaged, do have a limited service life, and a replacement can’t be economically/safely shipped from Necedah. Batteries are hazardous materials as shipped; they go by truck freight. And some of us bought pre-owned trailers (no orientation, maybe no manual)... there is no national dealership or service network... etc.
Those who can do swing by Wisconsin for service! Those who can do so learn from this site and other research. Others have hit & miss experience with finding good RV service locally. Good shops do exist. Batteries are trickier...
Disclaimer: I am not an electrical engineer, and knew very little about batteries in general, before I owned the CI. But after fixing a shorted wire, adding solar, a third brake light and a spare lithium portable, I know a little more about the trailer's electrics, and the battery in general. I'll try to reference and provide links and more authoritative sources. But anything you see here should be cross-checked for your purposes and peace of mind, before you follow through on any purchase or modification. There will be differences of opinion. But certainly I am open to being corrected on factual errors. Amongst us there will also be differences in OEM battery/compartment specs, so please take those into account as well. If you're short on time, you can also scroll to the end for a summary.
I'm also not going to recommend specific batteries or sources for replacement, since what worked for one person may not fit, or work, for another. Also... learning that one person got 8 years out of a particular battery is a great starting point. Replicating that feat 8 years later with the "same" product whose quality control may have lapsed within that time isn't a sure thing. The corollary to this is that a poorly performing battery may not be the battery's fault, since there's lots of ways you can unknowingly mess up a battery. Which is part of the point of this thread.
Sticking with a reputable manufacturer with a good overall track record, and judiciously matching up the specs of their current batteries with your own, is likely the safest route. Consulting with CI as to their current battery of choice will also likely serve you well. Since CI will have undoubtedly done their due diligence in this area.
OEM Battery Size and Compartment
For a long while CI has elected to go with a Group 24 size battery, although in the beginning they apparently used a 12V that was physically smaller than the current one. See Cary's clarification: Battery - Bigger Battery Although the currently used Group 24 is an industry standard size, not all manufacturers' batteries are exactly identical. Post type, position and orientation can be slightly different and make it problematic, and sometimes impossible, to install. Because the battery compartment is designed like the rest of the TD... i.e no wasted space... any prudent replacement should involve a careful measurement of what came out of your trailer (regardless of what I have written above), and to not try to exceed it with a larger battery, unless there's actual room to do so. Replacement with a battery whose terminal positions or design don't match what is already in there, or with a battery whose case is not a perfect rectangular box shape, can also be problematic . Modifications to the compartment to make things fit, aren't easy, fun or (possibly) pretty.
OEM Battery Types and Specs
This will vary slightly between owners and trailer manufacture dates. New owners of old CI trailers may not know what originally came with their trailer, or if what is in there now matches the original size and specs. My 2017 came with an Everstart Group 24DC "Marine" sealed flooded lead-acid "Deep Cycle" battery with 690 Marine Cranking Amps; CI had been putting this size into the trailer some time before that, and has continued to do so since. If not, then with an near identical facsimile. For about $100 more, CI continues to offer the option of an AGM battery upgrade, which is exactly the same physical size. AGMs are also lead acid, but are constructed differently, and mitigate some of the problems of misuse or abuse. (More about that later.) Their main selling feature is that for about an additional one half the cost of a new flooded battery, you can get twice the life expectancy: "AGM batteries typically have about twice the lifespan of our standard Deep Cycle (flooded) lead-acid batteries. The major factor determining long-life for any lead-acid battery is keeping the battery charged when it is in storage or during periods of non-use." (from the CI store page) .
Regardless of their AGM or flooded construction, OEM Group 24 lead-acid batteries are limited by basic physics to a rating of about 75 Amp/Hours. A/hrs are a rough measure of its overall capacity, and are akin to Watt/ Hours, which is another commonly used metric. W/hrs when divided by 12 = Amp/hours, when you a dealing specifically with a 12V electrical system. Larger Group 27 and Group 31 batteries offer tantalizingly bigger outputs, but they won't fit any stock CI trailer. A 75 A/hr battery will get the average user through about 3 days of dry camping using the lights, water pump, and fan, before it needs recharging. YMMV, of course.
Also, don't take other Group 24 manufacturer-stated A/hrs or W/hrs as gospel. There's different ways to measure that and many go for the one that looks and reads best. Make sure they are quoting the "20 Hour Rate", which is usually reserved for testing and rating Deep Cycle batteries, so you can compare apples to apples. The 100 hour rate is always higher, and would be misleading.
CI likely ended up on the current Group 24 sizing and A/hr capacity as both specs fit in well with their design, the overall economics, ergonomics, ease of future replacement, and the user needs of the vast majority of trailer buyers. Some forum members (including myself) for various personal reasons and needs, have opted to increase this respectable capacity in various ways, through the use of larger batteries, additional batteries, on-board battery systems with a different chemistry (lithium), solar systems and generators. Though frequently successful, sometimes this is achieved at considerable expense, effort, and occasionally, regret.
What is a Deep Cycle Battery?
(Here's what started my quest for the appropriate Deep Cycle battery replacement, and was ultimately the most confusing aspect of the hunt, for me.)
Basically, standard car batteries have more and thinner plates for the acid to work on. Resulting in a greater surface area and capacity to produce amperage. Which is what you need for turning over an engine: a short powerful electrical burst. It's a cheetah and will run out of steam in short order. Deep Cycle them and they will die. Not the best type of battery for a trailer, whose amperage demands are much lower and spread out over more than 4 seconds of cranking. Generally speaking, "Deep Cycle" batteries have fewer and thicker plates than auto batteries. You can draw more electricity from it, and over a longer time, before you start to change the internal chemistry and/or cause damage. Deep Cycle batteries are better for RVs and trailers. That's the basics.
Unfortunately, the term "Deep Cycle" gets thrown around. A lot. Most batteries that are held out to be Deep Cycle are actually a hybrid design, and are really meant for marine applications: they have to start a motor (i.e. have cranking capacity like a car battery) but also have to power things for a long time all on their own, like lights and trolling motors, when the main motor isn't producing electricity through the alternator and recharging the battery. Unlike car batteries, Deep Cycle/ Marine batteries can be taken down to about 50% Depth of Discharge (more later) before they have to be recharged. Perfect for marine applications. Nearly perfect for trailering, since we don't necessarily need the cranking capacity. But the cranking is there for us nonetheless. Especially if the Tow Vehicle needs a boost and you're in the middle of nowhere. However, a Marine battery is a hybrid, and as such, a compromise: pretty good at most things, an expert at nothing. Bottom line: if the battery or its literature states cranking amp specs in the area of 550 to 700, then it is a hybrid and likely will perform as a hybrid, and not a true Deep Cycle.
The RV and trailering community has had little choice but to rely upon the marine market for their trailer batteries. There are very few RV-dedicated batteries out there. However, marine batteries are easy to find and they generally don't cost an arm and a leg. But because they are ubiquitous, and are sold by many retailers whose main customer base is not specifically tiny trailers (i.e. automotive, hardware, solar, marine supply), they can also vary greatly in quality. So doing your homework is necessary.
A true Deep Cycle battery, on the other hand, has little cranking ability, but can be taken down even further than the 50% DOD on a regular basis, sometimes down to 20% or even 0% without damage. These are almost entirely designed and meant for the solar/wind/ industrial stationary market. Their sizes, shapes and oddball voltages, like 2V, 6V, 8V, make them generally unsuitable as a replacement in the current CI. There are however a couple exceptions; (more later). In truth, a true Deep Cycle battery for our trailer is exactly what it could use, to provide the greatest utility, speaking solely from an electrical standpoint. But because a true Deep Cycle battery is meant for stationary applications, its standard internal construction may not be robust enough to withstand the rigors of being jostled at the rear of the trailer, where vibrations and bumps are amplified. Even if it did fit the space, and even if it was the proper voltage.
What is Depth of Discharge?
It seems counterintuitive that a 12V battery that registers 11.0V could be "dead" and not provide any power to anything. But it is, and it may not come back to life either, or its original condition, even if you think that you have successfully recharged it. A fully charged 12V battery at 100% should read 12.7V to 12.8V. Immediately after charging it may even read higher than this before it "settles down". During charging, it will even read, and should read, in the mid-13's and slightly into the 14's. A 12V lead acid battery (Marine, hybrid or designated Deep Cycle) can be taken down to 50% of its capacity without doing any damage; this corresponds with a voltmeter reading of about 12.1 volts. Go below this Depth of Discharge (DOD) reading at your peril. I've attached at the end of the post a photo of a chart that I use for reference, and have taped to the right bin lid cover so I won't be wondering about how much juice I have left to play with.
To be fair, a voltmeter reading of an actively used battery is only a guesstimate of the State of Charge/ Depth of Discharge. The SOC is affected by ambient temperature and how recently the battery has been used. However, temperatures colder than 70 degrees actually provide you with a bit of a safety buffer, if you stick to the 12.1 cut-off. For accurate results, take the reading with no devices draining the battery. Better yet, wait an hour. Or take it in the morning after no battery usage for even greater accuracy.
Generally, no lead acid battery, whether flooded or AGM, should be taken below 50%. Seth, however, has located two batteries: Victron Super Cycle (not all their AGM) and some C&D Dynasty UPS batteries, whose literature suggests an occasional deeper discharge is not fatal, but is not really recommended either if you want to squeeze a maximum life out of it. These batteries are definitely the exception, and not the rule, when it comes to a Deep Cycle lead-acid safe DOD. Some Rolls and Concorde batteries may also be in that category.
The flip-side of the deep discharge is that repeated shallow discharges (less than 10%) can also be damaging and negatively affect service life. So it is a good idea to take the battery out for a "run" every once in a while, especially if your camping style is always established campgrounds with electrical service.
It should also be noted that a 50% DOD limitation also corresponds with a battery that can now only perform half of its stated A/hr rating. If you have added up all the amp draws of all your devices, and calculated your A/hr needs to be 100, for example, you will require a 200 A/hr battery to get all the work done. Correspondingly, our 75 A/hr trailer lead acid battery can only give us 32 A/hrs of work before it needs to be recharged, or before we do damage to it. This could impact your decision as to whether or not a single Group 24 battery is sufficient for your needs.
When assessing your battery's condition, a TriMetric Battery Monitor can also help you figure out what's going on with it, in certain areas that a simple voltmeter can't: Teardrop Travel Trailers by Camp-Inn , Trimetric - on a galley door?? , Best Battery Monitors for RV's, boats,off-grid cabins, vanlife
Leaving your 7-pin connected to the TV while parked or camping, and using your trailer's 12V system, can present a problem for your TV's battery depth of charge. There will be a drain on your TV battery, which is far less tolerant of deep discharges. You'll be taking both batteries down simultaneously, and your TV battery may not have enough juice to start the TV. A battery isolator, either installed on the TV, or the trailer will prevent this in the event you forget to disconnect. Teardrop Travel Trailers by Camp-Inn , Isolator - Battery Isolator
As far as what to do between trips? Leave the trailer plugged in and charging and it will be happier. Any lead acid battery will have a natural discharge rate, even if disconnected from the trailer wiring. Leave the main switch "on", and not charging, and there will be an even further "phantom draw" on the battery. Subject to other and plentiful variables, including age and temperature, a battery could easily self-discharge to the point of damage after only a couple months of not being plugged in to the wall: Battery Care Between Trips. As Cary states, leaving it plugged in also verifies the proper functioning of the charger at any time, with a peek.
There's lots of data out there about DOD compared to the number of full cycles in a battery's lifetime, and getting the most total A/hrs out of your battery, blah blah... A good basic rule is to simply stay as far away from the 50% as best you can, topping up completely whenever you can, and occasionally letting the battery actually do some work. And your battery and wallet will thank you.
What is the Difference Between a Standard Flooded and an AGM Deep Cycle?
In addition to the cost-vs-life-expectancy differences/advantages I touched on above (you'll have to do your own math on that, and with what is available in your area, on sale, or through a CI install, etc...) there are some other differences between the two batteries where some may find an AGM to be to their benefit:
1) AGMs are far less prone to leakage and spillage.
2) Because of their construction, they are even more robust than other Deep Cycle /Marine/ RV flooded batteries and more resistant to the jostles of the road.
3) An AGM may also be more tolerant of partial discharging, followed by a partial recharge.
In a partial recharge (less than 100%), followed by a discharge, a standard flooded lead acid battery can be prone to acid "stratification", which (to be very brief and non-technical) isn't a good thing for the life expectancy of the battery. When connected to the campsite post, it's not difficult to get a 100% uninterrupted recharge. On the road this can be a different matter, depending upon the abilities of your TV alternator. Many new 'smart' TV alternators can only take the trailer battery back up to 85% while on the road. See this about the CTEK device as a solution for this problem: Teardrop Travel Trailers by Camp-Inn and any other CTEK-related posts. Essentially, a CTEK will regulate and optimize recharging from multiple and simultaneous sources (TV, solar) to achieve a 100% battery recharge.
Uninterrupted charging all the way to 100%, by way of solar alone, can also be difficult to achieve, for reasons of cloud, shade or lack of sunlight. So stratification can be a risk with independent solar systems, and flooded batteries.
I really don't want sway anyone one way or the other, but AGMs certainly seem to have the upper hand. Particularly if you factor in the consideration of fewer replacements, and less environmental waste, since with care they can last twice as long.
If you do go with flooded lead acid battery replacement, make sure that it "sealed". That is to say that it requires no upkeep (water top-up) or venting, which would be evident by a series of removable caps. The battery compartment is too confined to support a vented battery and would collect the gases, which would be dangerous. AGMs by their design are sealed, which will always negate this concern. A sealed flooded lead acid battery is sometimes marketed as a VRLA (valve-regulated lead acid) but it is the same thing.
Get a battery that 'just fits'. Too small a battery will deprive you of amp hours as well as possibly cause damge to itself or the compartment by bouncing around. (Replacement battery - where to buy?)
I've Already Tried Camping and I Want 12V Power For longer Than The OEM Battery Can Provide; What Do I Do?
Between the 75 A/hr battery, 100% road charges in between destinations, and the occasional/frequent use of electrical sites, most of us will have the capacity to stay above 50% DOD almost all the time. But sometimes some of us just need more. Some like to get away from everyone, and boondock, for a long time. Others want to run a lot of hungry devices, or power a fridge in hot weather. Some absolutely need supplemental and reliable power for things like a CPAP. The trailer battery alone will either be severely challenged, all the way to grossly inadequate, under some of these conditions.
Each of these following mods/add-ons that are designed to provide more power to your rig, has its benefits, costs and disadvantages. But you could:
1) Install a Lithium Battery, that can be cycled below 50%. This comes with a complete re-think of the trailer's capacities, including a replacement of the OEM charge controller. As well as extra cost. But it can be done. Several forum members have travelled this adventurous road and enjoyed the journey: Good Discussion Of Lithium Batteries , Battery - Agm Vs Lithium. and Lithium Battery Charger
2) Carry a spare battery. This is an additional Group 24 battery that you can travel with fully charged in the TV, and replace with the OEM in the compartment when necessary. It's heavy. And safe, convenient transport can be a challenge. As well, there is the cumbersome act of switching out 50 lb lumps. Alternatively, you can connect it via one of the trailer's 12V sockets, without installing it in the compartment. Provided you disconnect the main battery first. An adequate gauge 12V to 12V 15A protected connection is required.
3) Carry a portable lithium battery station, like a Goal Zero. This much lighter option (than comparably sized lead-acid) requires no additional trailer wiring or devices and can plug directly into the trailer's 12V sockets (as above) with the proper connections and the mandatory main battery disconnect. It can power or recharge other devices, like fridges, well away from the trailer. Or elsewhere. Good feedback of usage and capacities through LED displays, with multiple recharging options. Can be costly, if you go with a quality unit: Good Discussion Of Lithium Batteries
4) Install a solar panel, either portable, or mounted or hardwired. (lots of good info and experience on the forum with equally intriguing and variable configurations)
5) Connect a gas generator. To either power or recharge your 12V devices or recharge the trailer battery through the 120V rear plug. This will also give you some 120V service separate from the trailer, depending on the size of the unit and your inverter.
6) Operate the Tow Vehicle for a short period to recharge the trailer battery.
7) Install a second battery in the trailer in parallel. Very few will try to convince you that this is a good idea. If it was, it would be a CI ordering option for those who want or need more capacity; it isn't. There is little room for such a modification, and for a variety of technical reasons CI has many times advised against it: Battery - Bigger Battery , Adding A Second Battery
8) Install a single larger battery to get more A/hrs, taking on the necessary 'challenging' modifications to the battery compartment: New Td Battery On Its Way. Read Seth's caveat about his project in this: Battery - Agm Vs Lithium
9) Install, or carry, a 'Pony Battery'. This is an auxiliary sealed lead-acid battery, which can be of any size, not just a Group 24. It can supply supplemental power to any device, like a fridge or CPAP, directly, provided that you understand what is going on with it's rate and depth of discharge. Unlike options 7 and 8 which are hard-wired into the trailer's existing system, charge controller and meter, a pony's wiring (if any) is distinct from the trailer's wiring. However, it can be used to power all the trailer's lights, pump and fan through a 12V socket... much like the options 2 and 3. Again, when doing so, it is crucial to disconnect the main trailer battery, or risk disparate simultaneous draw-downs, back-feeding and blown fuses (Thanks for those corrections, Seth) Cpap Power For Boondocking
With Options 2 and 9, you now have to come up with a recharging solution, for your depleted supplemental lead-acid, or resign yourself to carrying around useless weight for the remainder of the trip. Not an insurmountable task by any stretch. There are solar solutions, and some members (I believe) have modified their tow vehicles with additional on-board battery charging, though you want to make sure that your TV alternator is up to the task: Auxiliary Battery For Refrigerator Adding another 120V charger dedicated to the pony is also an option. But this is where Option 3, that has its own on-board charge controller, and which can be recharged from multiple sources (TV 12V, solar, 120V), has a distinct advantage.
I Didn't Really Want To Read Everything Up To This Point. What Are The Take-Aways?
I've undoubtedly missed some things, but I believe the following to be good and true advice:
1) Carefully measure your space and old battery before buying a new one. Look at the terminals/posts, their placement, and type. There's lots of different configurations. Most Group 24s will work, if that's what you had before. But measure anyway. Take into account the posts when reading the manufacturer's measurements. Too small a battery is also not good, as it will short-change you on A/hrs as well possibly cause damage to itself or the trailer if not secured.
2) Consider an AGM, either with your CI order, or aftermarket as a replacement. Properly cared for it should provide better service, utility, on a number of different levels. And better long-term economy. If you're really bad at looking after things, then maybe a more expensive pet like an AGM isn't the best idea.
3) You will likely end up with another Marine Deep Cycle battery as a replacement when the time comes. Make sure it is a quality one so that it in fact can handle the Deep Cycle part of the equation. The better it is at cranking, the worse it will be at the other.
4) If you want one that will do better than a standard Marine battery, and are jonesing for a true deep cycle battery that fits the battery space and can go below 50% DOD, really do your physics homework, study the spec sheets, and crunch the economics numbers as well.
5) If you have anything other than a lithium battery, which will be almost all of us, don't go below 50% DOD, or 12.1V. If your trailer doesn't have a battery monitor, or voltmeter in the right hand bin, get one. Or learn how to use a hand-held meter with the battery terminals or the 12V sockets. One or two deep unintentional discharges and you could be be several hundred dollars to the poorer. Or in the dark.
5.1) Keep your trailer plugged in and battery charging between trips. However, an always full battery isn't always good either. Occasionally let your battery naturally discharge more than 10% (or actually go out and use it!) to prevent damage and prolong its life. When camping, remember to always disconnect from your TV, unless you have a battery isolator. Then don't worry.
6) If you have a flooded lead acid (not AGM) and a newer vehicle, consider a CTEK as a way to get full charging on the road, and guard against stratification damage caused by partial charging. Consider it, even if you have an AGM, just so you are always topped up to 100% after coming off the road.
7) If you can, get as many trips in under varying travel conditions, to determine your electrical needs before you pull the trigger on something different than the OEM battery. Monitor your battery draw-down (how close you come to 12.1V) and/or calculate your projected A/hrs required with all your devices and on-board power draws. You might be surprised at how little you actually use, and that the OEM type of battery is more than adequate for most of your needs, most of the time.
8) Rather than attempt an oddball battery replacement to improve upon the trailer battery's capacity, consider one of the many other add-on solutions. Many of us who have attempted supplemental power are more than happy to advise what went well, and what went sideways, with our various projects/obsessions, and how to pull them off, so that you have all the power you need, or think you need. And then some.
In addition to the forum, CI's site, and other members' valuable and knowledgeable contributions and experience through the years, I also drew from the manufacturer's sites of high-quality batteries (like Trojan, Concorde and Rolls), and these more generic sources, among others:
Replacement battery - where to buy?
Basic to Advanced Battery Information from Battery University
Water Loss, Acid Stratification and Surface Charge - Battery University
Learning Center | Northern Arizona Wind & Sun
If I am off-base with anything or have misinterpreted information, please let me know and I'll "unsend" and correct the text. That way no one has to scroll any further to find the right info.
Thanks,
Steve
(If I've saved only one battery from an early death... it will have been worth it.)
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