New alternator and battery. Why does my car keep dying?

Correct. I have checked all connections to make sure nothing is loose. There are no signs of corrosion. The voltmeter does NOT read 13-15 volts at the Battery terminals. The voltmeter reads about 11.5V at the terminals after being jumpstarted and the volts continue to fall until the car eventually dies.

once the battery gets that low,it is completely DISCHARGED,and the alternator WILL NOT recharge that battery!..you will need to charge the battery with a battery charger to get it back up to 12.6-13.00 volts!

Thank you. I will try putting the battery on a charger ASAP and see if that helps. Is that really a thing? The alternator won't send a charge to the battery if the battery is too low? Ive never heard of that. I will let you know if that works.

unhook the battery cables before charging it.and no,you should see the alternator output around 13.0-15.0 volts DC.like i said you have a short to ground somewhere or that new/reman alternator is bad.anytime you buy an ALT,STARTER or anything electrical from a parts house like the ZONE,get them to check it before you leave, always!

I have bench tested the alternator and it is good. I will disconnect the battery before charging the battery. If the problem is a short how would I go about tracking that down?

i would start with the alternator wiring harness first,and check that big red wire that hooks to your alternator also...post results...

Check for alternator output at the alternator to determine if the power loss is before or after the alternator. If you have that 13-15 volts at the alternator that reinforces the short to ground. If not, the problem will be with the wires coming to the alternator. This should reduce the number of possibilities a little.

Thank you but it is very hard to check the voltage at the alternator. The power side to the alternator is a plug and not a screw on wire like I am used to. Not sure how I would use the voltage meter on that.

I'm having the same problem with a Hyundai Accent. Just charged the battery properly, started it once, and it lost charge overnite. Shows after market wiring for a sound system...so..short to ground?

I have replaced everything in this thread. I have no clue where else to go with this. New alt. New battery new computer. Guess it's time to re wire it! Any other suggestions?