Dual Battery Wiring

[Marsbar]

I have on all my 4wd's for the last 25yrs used a system of using the constant rated 200amp solenoid to do job, but have always wired the positives of both batteries together.

The reason I do this is when switching positives, arcing across the solenoid contacts can course a voltage spike that can damage electronic equipment. I also use a push button switch & pick up the positive feed from the second aux start battery to activate the solenoid when the start battery has been flatten. I never use the aux start battery to power any equipment so I only use a small battery(33amp SLA/AGM, tho it's big enough to boost start).
Because its small I can custom mount it just about anywhere in the engine bay & they can even lay on their side(SLA=Sealed Lead Acid-Valve Regulated). I have always custom made the mount for the main starting battery & used a bigger size than standard.

I have two 75amp Aux Deep Cycle Gel batteries mounted in the back of my truck to run the frig, inverters(1x300w, 1x600w), laptop, multi-media system, 2TB Hard drive with all my movies + LED worklamps etc & wire them in the same way(switch them using the negative/earth).

I couple them into the system via 50amp Anderson plugs so I can remove 1 to run the frig back at camp & I charge the other while I'm wheeling, These batteries have the same setup of switching the negitives/earths & any accessories I'm running off them are wired above ground so wont draw any power from the main starting or backup aux start batteries.

All this might sound difficult but its not rocket science but it isn't

[93xj97347]

I'm putting in a second battery in the back of my jeep. Can I hook the ground to the body or do I have to ground it to the motor? I have upgrade my grounds to the body already.