Battery Grounding

[spanky the wondermuffin]

it depends if you want both batteries to run the starter.if no,buy a heavy duty battery isolator kit.make sure it is rated for the output of your alternator.if you want both to crankthe car painless has a dual battery set up that use a big relay to connect the batteries.i have one in my tow rig.don't think you need it for a car.grounds can go anywhere,but the safest way is to tie them together and run them through a shut off switch on your dash.use a dual pole switch and isolate your alternator with the other pole.if batts. are in the trunk run oo (double aught) cable.your local parts house like napa should have cable,ends,and a crimping machine.i think it is worth it for the couple buck they charge(if at all) for a nice machine made crimp.are you putting them behind your seats?i had my (one) battery behind the pass.seat,but put it back into the trunk after a season.it's a big chunk of movable ballast,and i need rear weight.finishing the car,putting it on wheel scales,then moving them around until you found the most advantageous spot would be ideal.don't forget to size your alt wire based on output and run length.i use 4 gauge with a 150 amp fuse.i also use a furd style starter relay.the batteries need to be the same size and age.if you manually disconnect them from each other or ground upon shutdown you don't need the isolator.why 2 batterties?

[jeffandre]

Spanky,
Thanks for the info, I'll be using it this week as I continue designing the battery setup. I decided to use 2 Odyssey PC-680's (12v, 7"x7"x3" thick) and mount them directly under the seats. The area from the car floor to frame edge will allow me at least 1/4" of clearance once I install the steel boxes that hold the batteries. This will move the weight very close to center, just makes it tough to maintain without lifting the car in the future.

I have a lot to learn in this area, was hoping to get the batteries installed over the next few months as well as figure out whatever other gadgets I need to optimize the system for future use.