Ok, so here is Mick's 'brief' write up! Goodness!
Backup Battery Setup
Usual disclaimer, this is how we did it, not saying it’s the right or best way, just what we did.
The basis of our setup is a switch that enables two separate power sources or connects two sources, more on why you might want to do that later. The switch is the Blue Sea Systems 9001e e-Series Battery Switch Selector, see below for the details. Basically it has three connectors on the back, the single output which is the trailer main power feed line. The other two are input sources, one for the main source which would be the battery already in the trailer, a second for the backup source input.
To setup the switch you first disconnect the wire that goes from the trailer +red battery to the main power distribution block. The wire you are looking for has an inline fuse on it. The trailer power line connects to the output of the selector switch.
You now need to create a new wire that goes from the trailers battery +Red terminal to the input #1 on the selector switch.
OK, so basically that’s it for the trailer power hookup, set the selector switch to #1 and you connect the main trailer battery through to the trailer.
The pic above shows where we mounted the switch. Next to it is the second part of our solution; it’s a Warn winch mount kit connector. I purchased the WARN 70920 Multi-Mount Wiring Kit as it comes with a short wire with connector which I used for the trailer side connector and a long wire with connector which I will show later as it makes up the external battery backup setup. What I like about these connectors is that you can buy them pre-wired and you can get a nice 4 AWG wire meaning no volt drop across the connection. Refer back to the wiring diagram for this part. The +Wire of the Warn connector is connected to the #2 input of the selector switch. NOTE, the BLUE wire is the +Positive. The –negative Warn connector wire, the yellow wire, is connected to the trailers black –negative block. You can connect it to the –negative black wire of the trailer battery. All the –negatives connect to each other.
These Warn connectors are designed for winches so are pretty robust.
At this point the trailer wiring is basically done, as you can see it’s actually very simple. Now with the selector switch in position #1 the main trailer battery is powering your trailer. In position #2 the external power source which you connect to the Warn connector powers your trailer.
OK, so lets quickly discuss why we installed a complete disconnect system like this. I originally wondered if I could just plug an external source into the 12v socket in the galley. The problem with this is that if you plug into the 12v socket without disconnecting the dead battery all you will end up doing is draining your backup battery as it balances the drained battery in the trailer. The dual switch as described above enables the aux backup battery to be connected and act as a totally new battery powering the trailer without being drained by the onboard battery.
Onto the description of the external source, we chose to go overboard.
(Sarah says, "Big surprise here! Sheesh!")
We chose to purchase a battery box, the MinnKota Trolling Motor Power Center and put a big battery in it, Universal Power Group 45978 Sealed Lead Acid Battery. The reason for this battery box is that it has integrated fused connectors. It has 60 Amp terminal connections and 10 Amp 12v sockets. The big sealed lead acid deep cycle battery fits in it even though it’s not listed to. Trust me, it does. I did connect a couple of other things to the battery box so for a basic setup ignore the charger on the side and the inverter on the front. Oh, it’s super heavy, do not use the handle on the top of the box, use the side connectors.
The other side of the Warn connector wiring kit connects to the battery box. I think I cut off the connectors supplied on the Warn wires and crimped on 4 AWG lug rings, which I think I drilled out a little to fit the terminals on the selector switch and the battery box.
When you plug in the aux backup battery you set the selector switch to position #2 and the main battery is disconnected and the aux backup battery powers your trailer. As the trailer battery is disconnected it will not drain your aux backup battery.
The selector switch also has a 1+2 position. If you select this position you do connect the #1 input with the #2 input, which is connecting the trailer battery with the aux backup battery. In this mode you could use the trailers battery charger to charge both batteries, assuming you are plugged into shore power, 110v and you have the CampInn built in 5amp battery charger.
I wanted to use the little aux backup battery box for more than just trailer backup power. This is actually the third 12v battery power box that I have built and I think this is my best so far. The trolling motor battery box is great when combined with the big battery. I then added to that a battery charger, the Battery Tender 022-0157-1 Waterproof 12 Volt Power Tender Plus Battery Charger, which is the same charger the CampInn uses. I have many of these to charge my race car batteries. I hard wired it to the battery. On the side I connected the Xantrex Prowatt SW1000 1000W True Sinewave Inverter, so that you have not only 12v on the battery box, but you also have silent 110v. The true sinewave inverters are expensive but they power more sensitive equipment such as our espresso maker which I would die without (Sarah- "it seems our Bialleti isn't fast enough!"). I’m not going to go into what type of 110v equipment you can power with one of these inverters or for how long, there is many web pages that go into detail on how to calculate that. The battery that we chose to use in the aux setup is 100ah which is actually more amp hours than we have in the trailer, even with the extended battery setup that we did.
That’s about it, have fun. -Mick
The funny thing is that as I wrote this I realized that as usual I forgot the KISS rule. I had considered doing the simple setup, same as what Frank is doing. His setup disconnects the main battery so when you plug into the 12v socket you are just powering the trailer and not connecting batteries. At some point I decided I wanted to do a dual switch setup, I'm sure there was a reason at the time (Sarah-"it is because he is More-power Mick and everything is overkill!").
The basic parts list for this build
Blue Sea Systems 9001e e-Series Battery Switch Selector
http://www.amazon.com/gp/product/B000K2MCR2/ref=oh_details_o01_s00_i00?ie=UTF8&psc=1
WARN 70920 Multi-Mount Wiring Kit
http://www.amazon.com/gp/product/B000OV9NGC/ref=oh_details_o09_s00_i00?ie=UTF8&psc=1
MinnKota Trolling Motor Power Center
http://www.amazon.com/gp/product/B001PTHKMG/ref=oh_details_o02_s00_i00?ie=UTF8&psc=1
Universal Power Group 45978 Sealed Lead Acid Battery
http://www.amazon.com/gp/product/B0044Z8DJW/ref=oh_details_o03_s00_i00?ie=UTF8&psc=1
Pico 4239C 4 AWG Battery Cable 3/8" Tubular Lug Ring / Eye Terminals 15 Per Package
http://www.amazon.com/gp/product/B00030CY5G/ref=oh_details_o09_s00_i00?ie=UTF8&psc=1
You will also need some wire, I recommend 4 AWG
Optional for the Aux Backup Battery Box
Xantrex Prowatt SW1000 1000W True Sinewave Inverter
http://www.amazon.com/gp/product/B002I04A74/ref=oh_details_o01_s00_i00?ie=UTF8&psc=1
Battery Tender 022-0157-1 Waterproof 12 Volt Power Tender Plus Battery Charger
http://www.amazon.com/gp/product/B002DU3S9A/ref=oh_details_o00_s01_i00?ie=UTF8&psc=1
