I recently installed some PIAA lights (4) and the truck sat for a few days. When I went to drive it the batt was dead. Did the slow trickle charge and drove it for a few days noticing hard starts due to low voltage. After sitting again for a few days the batts were dead again checked voltage and the driver had 12.5 while the pass only had 6.5. Did I hurt something while charging or did my batts go bad. Alternator seems good b/c when I drove it there was no voltage drop. Please help gurus!

 

My guess would be that you have a battery failed. That would explain the difference in voltages, where a charging problem wouldln't.

 

Thanks for the reply. Thats what I thought, switching bad one out tonight. Any thoughts on how much stereo and lights would draw on factory alt. b4 needing a larger amperage one.

 

If you your Piaa lights are 100 W units at 12 V each will draw approximately 8.33 A (33.33 A total).

If they are 65 W units at 12 V each will draw 5.42 A (21.66 A total).

You should have enough capacity in your factory alternator to handle the lights provided you don't just drive short distances with all of your lights and accessories on.

If your alternator cannot keep up with the electrical load it will not reach the intended 14.4 V while the truck is running above ~1000 RPM.

 

Your pass side battery is not getting any charge because of a bad conection or cable.
Fix that first to see if your pass side battery will come back to life.
12.7 is a good battery and 12.1 is a dead one 1
The batteries in this truck are hooked in a parallel curcuit and you should always get the same volt reading on each side because of these large cables that are in parallel
Your alternator could handle a dozon of those lights even at an idle.
You should get a minimum of 13.8 on both batteries when the truck is running