Dual Battery Setups - Dual schools of thought...

[tribri1]

Hey, I am looking at adding a second battery to my rig for running accessories when the ignition is off. I plan on going with a battery isolator but want opinions on how to set it up.

First school of thought is link the batteries and have the accessories run off the main starter battery. The second battery is used only as a backup in case you drain your primary battery below starting levels. When the engine is running both batteries are charged. Basically with this system you do everything on the primary battery and jumpstart your rig with the backup if needed.
Pros: Easy to wire new battery.
Cons: Can't think of any, the second battery just sits there. Maybe if you primary battery is getting old you will not realize it until both batteries are dead since the system automatically kicks in the second battery when needed.
Example: http://www.painlesswiring.com/webcatalo ... All=Trucks

Second School of thought is use your primary battery for starting and for accessories when the ignition is on. Switch the system to the camper battery when the ignition is off. Again both batteries are charged when the engine is running. Depending on the location of the second battery you can still use it to jumpstart a dead primary battery using jumper cables.
Pros: Your primary battery is always charged and ready to use to start your rig. A dead second battery does not affect any starting operations.
Cons: Harder to wire up, the accessories need to be wired through an accessory fuse block connected to the second battery. Depending on how extensively you want to wire things up (radio, dome lights, etc) this could be an undertaking.
Example: http://www.warn.com/atv/accessories/dua ... trol.shtml

Of course there is the third school of thought which is wire up two parallel systems with a toggle switch and make the battery change manually.
Pros: Easy to wire, easy to know which battery you are draining when the ignition is off. Cheap!!!
Cons: If you are running a fridge or other continually running device you have to remember to switch the batteries every time you stop for an extended period of time. Big ugly switch...
Example: http://www.pirate4x4.com/tech/billavist ... _setup.htm

I am planning on running the stereo, a fridge, 400w inverter and a few aftermarket interior lights. I am leaning towards a dedicated camper battery and dedicated starter battery.

I would love to know what you have done, how your RV is wired and additional pros and cons which I did not think of. Any thoughts and corrections on grammar strongly encouraged...

[MountainManJoe]

Use a solenoid separator instead of isolator which has too much voltage drop, charges poorly, and wastes energy as heat.

Don't run accessories/appliances on your main starting battery. It was designed for cranking and that's it. Deep discharge will destroy it. Get a proper deep cycle battery.

If your fridge is 120V, you'll need a lot more than a 400W inverter.

[tribri1]

Thanks for the advice, the fridge is 12v. the 400w inverter is for charging the laptop, camera, gps, etc. Just little stuff and not very often.

[doyoulikeithere]

I liked option 2.
wire your radio to the camper batt and dont use the dome light for the interior much if you have some other lights.

[1Gary]

My Winnie is wire for a starter battery only and I added a second deep cell battery for the house.The deep cell batteries have a momentarily switch in the overhead to use if the starter battery goes dead.The frig is three way.A/C-D/C-propane.Those are big $$$$$$$$.

[Coyote X]

The easiest way to move a circuit over to the second battery is to pull the fuse and use a spade terminal to power the circuit through the panel. That way the fuse could be put in a secondary panel powered by the spare battery. On mine I used a relay to the acc position on the key to turn the secondary panel on and off.

That is how I got my windows to roll down in the acc position

[tribri1]

Nice tip coyote x, I will put some thought to that too. Another thought is if I had 2 deep cycling batteries then I could go with the first option where the primary battery is used for everything and the secondary is used as a backup and is only used if needed to jump the primary.

[Herbie]

Take a look at my build thread (in my sig) for my dual-battery setup, but basically I did your Option 2 and run most of the accessories off the house battery. The van's dome lights have been re-circuited to run from the house battery, but the radio has not YET been done, so I have to be careful with the radio when parked.

For me, swapping in a spade terminal into the fuse block (as Coyote X suggests), or "reversing" one of those add-a-fuse inserts that's meant to add a new parallel fuse into a block, is probably the way I'll go, I just want to be sure that the Retained Accessory Power system will still work correctly.

[MountainManJoe]

I did the reverse. I connected the entire underhood fuseblock to the deep cycle. Like that, everything except the starter motor and alternator are connected to the house battery.

THEN, I used ATC fuse taps in reverse (a la Herbie), and modified MAXI fuses (because I couldn't find MAXI taps), to connect the starter & fuel pump relays to the starter battery. That way you can still start if the house battery is used up. Also, if I ever decide to sell, or just return everything to factory config, I don't have to do any re-wiring. Just pull the taps. I'm posting a write-up on this soon.

[MountainManJoe]

I sketched a simplified diagram of my setup. Sorry about the quality. If you need anything clarified just ask.

I used 1/0 AWG welding cable to connect the batteries and inverter.