Charging problem

[Jeremy09]

Thanks alot man

this sounding more and more like a regulator problem, or possibly a battery condition issue.

He has a single northstar 76ah battery. I got a single xp3000 120ah battery..both bats rest at 12.8v

both at rest showing 12.8v is one thing. a battery with a defective cell under zero load will show proper voltage when it's just got some charge from the alternator.

as a q&d test of the alternator and regulator.
start the vehicle, and disconnect the + terminal. if the car continues to idle and you hear the idle speed go up slightly alt & reg working fine.

to test if it's the battery that has a weak or defective cell
if you can get your hands on another battery with similar capacity that you know is in good condition, switch them and see what happens
or
disconnect that and yours from the terminal, and note the resting voltage of both. add a high draw load for 2 minutes on each battery, checking and taking note of how long each battery takes to drop down to 12v. if yours drops down to 12v significantly faster than the other, and when the load is removed it takes longer to get back up to 12v, you can safely assume its discharging too quickly, probably because of a single cell being defective for some reason.

hope you gt.