Battery Issue

[locknload]

I have a stock front battery and stock alt with a Kinetik HC 800 in the truck with 1/0 connecting them. I have had it this way since December and had no problems till now. I was driving around and my one amp cut out, so i pulled over and checked the voltages of the batteries with the car off and then with it running to see if there was something wrong with the alt, everything is sitting fine except that the rear battery is not charging when i have the amps hooked up. If i just take the wires from the front battery and hook them to the rear battery everything works great, it sits at 14.5V just like the front. But as soon as the amps are hooked up the voltage of the back battery drops to around 12V with the car running and if i watch it with the DMM i can see the voltage dropping even lower. The Front battery stays at the 14.5V when i hook all the amps up. I have checked all the fuses and such but i cannot figure out why this is doing this, nothing on the car has changed in months.

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[Pioneer~Saturn 5,000+ posts]

Pics of wiring/diagram of how you have it hooked up?

 

[NewAgeKing 5,000+ posts]

Battery could be shot. It will sit at a higher voltage but once it has a load on it she will drop.

 

[locknload]

I Have the big 3 done in all 1/0, a single run of 1/0 for the ground running from the negative term on the front batt to the negative term of the rear batt. Then i have a run of 1/0 from the front batt positive term to a fuse up front then another fuse in back before it goes to the positive rear batt term. From the rear battery i have a piece of 1/0 from each term to separate distros, that splits it to the amps.