New Alt and battery but wont hold a charge

ok so let me set the tone for you all...i was cleaning out my truck with the radio on and doors open and went to start it and NOTHING. The lights and radio would turn off when i tried turning it over so instantly i thought of battery...its the original battery and has probably seen better days so i may as well get a new one...so i get the battery(carquest $50) and install it...noticed my battery gauge would never go over 12v after that and when i gave it gas the brake and battery light would come on. so i then figured the alt to be the problem so i went and got a new altenator(advanced auto $150.00) so now im thinking my troubles are finally over i jump started the truck and let it run for a good hour or so to top charge up the battery a bit...i turn off the truck and tried to start it again NOTHING. i checked every source wire from the alt to the battery and got juice from all that i should...but one the red and white lead that goes to the ecm i believe...got no juice from that at all(should i ?) when i probed it with the light it did make for a deeper cycle on the battery(instead of 12v it went up to 13.2) and the 2 lights on the dash seemed to have gone off...can anyone give me any insight as to what the problem may be ? i think the alt i got could be a defective one but not sure and cant confirm it without knowing if i should be getting juice from that lead or if i shouldnt.:banghead:

aftermarket amp or radio installed?

yes both but both were taken out of the loop

It's not unusual at all to go thru 2 or 3 of these parts store alternators and starter motors before getting one that works. It also would not surprise me if 3 months later your parts store alternator gave up its ghost either.

You mention that after you replaced the battery with a new one and you were getting only 12v and then you put a new alternator and let it run for a good hour. What was your battery gauge reading then when you have both new battery and alternator? Was it still 12v? If so then the battery is not getting charged up. With engine running and alternator working, you should get around 13+V on the battery terminals if you use a volt meter.

I would suggest to purchase a 120v portable battery charger/starter and re-charge your battery that way. It would kill your alternator if you used to re-charge a depleted battery. Instead use a 120v portable battery charger/starter to fully charge the battery.

As you the alternator will only recharge the battery at a certain rpm, so if you were just idling and not reaching the rpm required for the alternator to recharge the battery then you were just using your battery for that whole hour idling and drained your battery. Make sure your serpentine belt is not stretched out beyond it's specs. If you look on the serpentine belt tensioner, there will be an indicator which tells you that it has gone beyond its stretch mark or not and if it is then you have to replace the serpentine belt.

You mention that after you replaced the battery with a new one and you were getting only 12v and then you put a new alternator and let it run for a good hour. What was your battery gauge reading then when you have both new battery and alternator? Was it still 12v? If so then the battery is not getting charged up. With engine running and alternator working, you should get around 13+V on the battery terminals if you use a volt meter.

I would suggest to purchase a 120v portable battery charger/starter and re-charge your battery that way. It would kill your alternator if you used to re-charge a depleted battery. Instead use a 120v portable battery charger/starter to fully charge the battery.

As you the alternator will only recharge the battery at a certain rpm, so if you were just idling and not reaching the rpm required for the alternator to recharge the battery then you were just using your battery for that whole hour idling and drained your battery. Make sure your serpentine belt is not stretched out beyond it's specs. If you look on the serpentine belt tensioner, there will be an indicator which tells you that it has gone beyond its stretch mark or not and if it is then you have to replace the serpentine belt.


i agree aboout the idling part. you need to drive the truck--even if it is around the block 3 times or more...

checking the belt is good advice, as a stretched one won't allow googrip and may not be spinning the alt to full potential.

i agree aboout the idling part. you need to drive the truck--even if it is around the block 3 times or more...

checking the belt is good advice, as a stretched one won't allow googrip and may not be spinning the alt to full potential.

Drove the truck to parts store for new belt and terminals so that would have been sufficient to charge it somewhat...i installed a second alt with the battery being charged over night on a time delayed charging system and whammy!!! 14.7v on the meter truck started right up...all along it was 2 bad altenators (autolite worked perfectly!!!)

2 bad alts...that's a bummer, and a great headache...>sigh< quality control sucks these days