Dual battery setup anyone?

[chrisbmwe30]

Has anyone done a dual battery setup one under the bonnet one in the boot?
I'm looking to use an oe wire for the battery in the boot setup then still use the existing terminals/cables in the engine bay with some sort of isolating switch near the positive terminal of the battery in the boot.
I'm hoping to be able to run a small camp fridge off the battery in the boot without draining my battery under the bonnet for starting. Will the setup be this simple or will I need something else?

Any advice would be great.

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[jlevie]

Some vendors of thermoelectric coolers offer a battery saver, which will cut off the cooler before the battery is exhausted. That would be the least expensive solution.

[DaveSmed]

If you have your heart set on running the fridge on a separate battery, you could possibly greatly simplify the install if you narrow down what you want the battery to do. Namely, you don't need the giant OE cable running the length of the car to charge a battery, look at the size of the wire coming off your alternator for reference.

But if you intend to have it help start the car, that's a different story of course.


A simple setup for fridge use only would be something like 6 AWG wire coming off the back of the alt, to a fuse, to a decent relay (80-100amp range), to a deep cycle battery in the back with the fridge attached. Control the relay by wiring coil (-ve) to ground, coil (+ve) to the alternator's D+ terminal.

[Cephas]

I think you just simplify by going deep cycle battery in the oe spot. Add a battery saver and you're good to go.

[trippmann]

i think you could really simplify it by just getting a cooler with ice

[chrisbmwe30]

haha some good replies ^^^^
dave will using the oe wire still be ok as i have already purchased this? can i run my positive cable directly from the positive terminal in the engine bay to the boot? instead of from the alternator?

[DaveSmed]

haha some good replies ^^^^
dave will using the oe wire still be ok as i have already purchased this? can i run my positive cable directly from the positive terminal in the engine bay to the boot? instead of from the alternator?

Yessir, larger wire will never hurt. The positive terminal is fine as well. How do you plan on isolating the two? The relay idea I mentioned?

[frankenbeemer]

[ATTACH]73771[/ATTACH]

[chrisbmwe30]

Possibly just a simple isolating switch. Wired in nearthe boot battery. I considered an electronically controlled isolator but don't feel it will pay itself off.

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[DaveSmed]

http://www.ebay.com/itm/Bosch-0332-002-156-Relay-12V-75A-/300826262673

http://compare.ebay.com/like/261219521112?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar

Compared to

http://www.wholesalemarine.com/perko-250-amp-battery-disconnect-switch-for-12-24-or-36-volt-systems.html?utm_source=feed&utm_medium=cpc&utm_campaign=google&gclid=CMblpP2IpbgCFcuf4Aod1CwArA

Boils down to what you want. If you want to start the car from the rear batt, the disconnect is the better idea. If you want it for auxiliary consumer use, the relay is the better idea. The disconnect switch means you'll have to have a procedure to start your car from now on. The relay, nothing changes and it stays topped up automatically.