Measuring Battery Usage Question

For the batteries used in CI, can anyone tell me the relationship between volts and % battery life remaining? I've seen tables posted on websites, but didn't see any that matched up to a fully charge voltage of 13.1(reading of our battery when fully charged).

We are planning a 10-day camping trip and will be without electricity. We have the volt meter that came with the trailer. I'd like to use this to get more details on our usage.

Thanks,

 

Bob,
I think Camp-Inn recommends that you should not let the battery go below 10.8 volts. I think I read that here in the forum somewhere. Hopefully Cary or somebody else can confirm that or give you more wisdom.
Charlie

 

Thanks Charlie,

That helps. Below an example of a table I've seen. Anybody know if a similar table for the batteries used in CIs?


volts - % Remaining
-----------------------
12.63 - 100%
12.54 - 90%
12.45 - 80%
12.36 - 70%
12.27 - 60%
12.18 - 50%
12.09 - 40%
12.00 - 30%
11.91 - 20%
11.82 - 10%

 

Bob, when your battery is charging (shore power or tow vehicle) you will get readings from 13.1 to maybe even 14. These aren't true readings, because when you unplug you will get somewhere around 12.5 - so perhaps 12.63 at 100% is correct.

But you can safely go much lower than 11.82 - Cary told us it's fine to go down to 10.5, but not to go any lower. If you hit 10.0 you are damaging the battery.

 

Guys, IMO you are trying to make a mathematical equation for forecasting the weather. You're gonna get what your gonna get.
If you are concerned, buy the largest amp. deep cell battery that will fit and run it until the lights dim. You will be surprised how long it will last.We camped for a full week and it was still in the 12's. Just be a little frugal if going for a week or more.

Having your car hooked up to an isolator will allow charging at the South Pole as long as you have gas. Also if you are doing any traveling you won't have to even think about the battery.

I was paranoid at first, but the 72 Ah soon showed how good it was & that I didn't need a 100 Ah.

Hilditch

 

Not trying to predict anything (though weather forecasters use math models pretty effectively). All I want to do is take advantage of the voltage readings available to see if we are on track for the battery to last while camping 10 days in the same location. Rather than just using the meter dummy lights(high, med or low) I think it's helpful to know what percentage is left. It looks like this will be easy to tell.

Evan,
Thanks for the tip. I unplugged the trailer and the voltage reading fell to 12.6. So the table I found will work perfectly.

 

OK Bob, make a list of the variables and then decide how much you are going to use what based on their draw per hour. I'll guarantee it will last 10 days if you tweak it and handle it right with a 72 Ah deep cell or larger battery.

Hilditch

PS: Math models are not mathematical equations.
Also battery depletion is NOT a straight line.

 

Hildritch,
No intentions of doing any of that. I'm just looking for guidance on interpreting the voltage readings.

I started this thread after I read this article.

http://www.rvtechtips.com/?p=10

After I saw this article/recommendations, I wondered if the table they provided and overall recommendations might be useful for my battery as well. My 100% charge voltage didn't match the article, however. Evan's note cleared that up.

The battery tester that came with the trailer has green/yellow/red lights, but it also has voltage readings. The article says voltage relates to % battery remaining. I was just looking for some insight on how to interpret these voltage readings. That's all.

Thanks to all for your helpful replies.

 

Bob,

Keep in mind that the voltage reading is heavily affected by any load on the battery. If you turn on all your 12v gear, the reading will be much lower than when everything is turned off a few minutes later.

So, using the meter to calculate the remaining percentage of battery isn't going to be an exact science. The reading will go up and down depending on what is running at the time.

And, if you are running everything at once, it can dive from 11.0 amps to 10.0 amps in a second. That happened to us on our first night. In that case, just make sure you immediately charge it back up to minimize the possible damage.

I think if you use power conservatively, it will take quite a few days to even hit the low 11's. And as you can safely go down as low as 10.5 volts, you shouldn't generally have anything to worry about. Just keep an eye on it, and plug it in to an outlet when you store at home.

 

Hmmmm... I thought this excellent thread had pretty much played itself out, but now I just can't help myself. I have to add a question Evan's note brings up.

"[P]lug it in to an outlet when you store at home...."

Evan, how are these things wired? Are you saying the 12v system rides on the 110 system whenever it's plugged in? That would certainly make sense, I'd imagine. I would then further imagine that whenever it's on shore power it's trickle-charging, and thus your note? Is there a good voltage limiter/regulator/whatever included, then, to ensure it doesn't overcharge? (Ignore my faulty nomenclature here -- I became a CE because I didn't understand EE more than forty-five years ago).

According to the wiki article on lead-acid batteries (http://en.wikipedia.org/wiki/Lead-acid_battery), overcharging is very damaging: "3.Precise float voltage (±0.05 V) is critical to longevity; insufficient voltage (causes sulfation) which is almost as detrimental as excessive voltage (causing corrosion and electrolyte loss)." And even without the article to tell us, we techies all know about and have seen electrolysis at work, the hydrogen and oxygen bubbles coming off, etc., depleting the water and producing explosive gas.

I know the electrical power aspect of RV/trailering is a mature technology, so these things have all been worked out many years ago. But how is this particular 110/12-volt connection set up, and is months-long storage plugged in to shore power really the safe and recommended course?

(And an unrelated comment on the thread: Voltage reading is also dependent on temperature, the standard reading being at 68 degrees. If the battery is hotter or colder (from weather, or from recent load or charging), your voltage reading may vary).

 

Jim,
The camp-inn handbook will give you the wire diagram. As I remember my instruction and my reading the Classic and Ultra models are set to not allow overcharge. Page 15 in the owners manual describes it as an automatic 6amp charger. It goes on to say you can leave your Ultra and Classic plugged up full time without worry of overcharge.
Hope this helps,
Steve

 

Both Craig and Cary told us that leaving it plugged in for months at a time is the best way to keep it maintained. Cary is the battery scientist, so I'm sure he could explain in detail exactly how this works...

 

OK, guys. I never thought I had an answer, just thought the question should be asked. A bit over two weeks from today (August 4th!) I should have my very own 560 Ultra owner's manual and a chance to talk with the experts in Necedah one-on-one, so I'll be listening for that particular bit of info.

As an aside, I went against the experts' advice once already by ordering mine with the larger, 72ah battery, despite its bad rep for durability. Why? Because I want the option of adding a physically larger battery later, and they said the smaller battery comes with a smaller compartment that doesn't allow physically larger units later. Maybe I'll never need it, but batteries are really cheap, so if it conks in two or three years, RIP and I'll move on to something better.

 

I wasn't aware of the smaller compartment with the standard battery. If I'd known that I would have done the larger battery as well.

 

In the interests of complete accuracy, let me reword. Cary's February e-mail to me when I was deciding which to order didn't say the battery space for the standard battery was physically smaller. What he said was that the rear section is "built differently," and, "The larger battery cannot be installed in a trailer configured for the smaller battery." Here's his note on the topic:

"Standard battery. Yes, I have seen some customers eventually put in a nicer AGM or gell battery of some sort in place of the standard Larger battery we install (the standard small battery is already a high end AGM). That works out well. Expensive proposition, but for some it ends up making alot of sense. The larger battery cannot be installed in a trailer configured for the standard battery however. The rear section of the trailer is built differently to create the larger battery option. If that is a thought you are considering then you may need to go with the larger battery option to allow this sort of battery upgrading down the road."

I did, and do, interpret this to mean the space for the smaller capacity battery is physically too small for a larger battery later, but there are other, less likely, interpretations possible as well (e.g., substructure strength, cable arrangements, whatever).

And it would make sense that there may be another tradeoff to a large battery space. Since the overall trailer size is unchanged, something else has to be pared down to make up for any added volume in the battery compartment. You might (or might not) be able to tell what that would have been by inspecting your 560.

 

Although, with a good solar panel, battery size could be irrelevant - unless you are running a breathing machine all night. In this case, Cary recommends the larger battery anyways.

 

Evan

Are you saying that this is an accessory that you have not got on Snugglebug.

Is this a first

 

Yes - I've got the smaller battery.