What's the simplest, most reliable DIY dual-battery system?

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Been here a while
Posts: 119
Joined: November 16th, 2007, 12:29 pm

What's the simplest, most reliable DIY dual-battery system?

I'm in the running for a dual/Aux battery setup to run a few accessories (fridge & lights) from the car without flattening my main battery.

I want the altenator to keep the charge up to both of the batteries, but only let the Aux battery go flat when using accessories without the engine running (keeping the main battery good for starting the car).

I'm after something online if possible as the closest 4x4 specialist is about 1.5hrs drive away.
'03 Bravo 2500 4x4

Unread postby Renasc » December 28th, 2007, 8:58 pm

Posts: 7161
Joined: March 15th, 2007, 8:21 pm

200amp continous journey solonoid ( $30 from super cheap or off ebay)... like this DUAL BATTERY ISOLATOR SOLENOID - EASY TO DIY 100AMP ABR - eBay, 4x4 Accessories, Car Accessories, Tuning, Cars, Bikes, Boats. (end time 06-Jan-08 20:15:00 AEDST) it wires like a simple relay........2 outer terminals (large) A) power in and D) power out... 2 inner terminals b)to switched ignition source c) to earth...

b c

A) To Alternator charge terminal
b) ignition switched active
c) earth
D) To Aux battery ( thru fuseable link)

....( using battery starter cable)
A) to oem battery (+) terminal
b) switched ignition active
c) earth
D) to aux batt (+) terminal

I have been wiring up the first method with out issue for people for many years... i allows both batts to charge but be isolated when ignition is switched off..

the second method is usefull if needing the aux batt for cranking applications ect.....but it can be its down fall..if you have a starting issue and you have to use the starter for too long then you will just drain both batteries and wont know untill both flat...

As an extra to the 2nd way u can simply fit a piece of batt cable connecting both batt (+) together thru a red ket marine switch ... this is so you can simply hit the switch to act as a jumper lead if required....( note must have a heavy crank earth strap).. as i said b4 you cant flatten both batts unintentionally
thanks to... APM Radiators.. DRW automatics..Boss Racing Diffs..Sprint Auto Parts.. Bob Jane Marion..Noarlunga refrigeration..J&S Suspension (et4wd)..Heinrich Performance Dyno..

Unread postby toy yoda » December 28th, 2007, 9:23 pm

Been here a while
Posts: 119
Joined: November 16th, 2007, 12:29 pm

Ah, thanks for the info, that helps a lot.

'03 Bravo 2500 4x4

Unread postby Renasc » December 29th, 2007, 12:42 pm

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