Poor Man’s Dual Battery

ujtruck · October 23, 2012

Last weekend I installed my second battery, use 2/0 welding cables – rated for carrying over 500 AMPs and welding cable Lugs, I solder them because crimpers are more expensive

To isolate batteries install a PAC-500 500-Amp Battery Isolator Relay (Heavy Duty), but when its engage use less than 1 AMP of current.

How this thing work:

I didn’t run battery cables from second battery to main battery; instead I connect second Bat positive to Relay then to Alternator , Ground Cable from second battery to engine block – now relay has 2 more small terminals, connect one of them to second battery ground and other one to under hood fuse box – IGN/ECM fuse. When key is in RUN/START position relay is closed batteries are combined (help engine start/receive charge from Alternator)

And key is in ON/AUX position relay is open second battery is isolated, means now I can use radio, lights etc without fear knowing that second bat is fully charged and waiting for my command.

I ran my truck full 8 hours, no issues, codes etc.

Factory wiring is untouched