i had group 34 red top up front, and in the back it was a bigger group size, iirc the back redtop was 950-1000 crank amps. Dual 1/0 power runs with a chasis ground, dual 1/0 for the big 3. stock 90amp alty. I rarely ran it full tilt without the rpm's up 2k-3k. With the rmp's up a little i could maintain 12v at full tilt.