Battery keeps dying but battery and alternator checked out ok!
 

This is on my Automatic 2000 Coupe. I’ll try to describe my problem the best I can. I bought a new 7 or 8 year battery about 7 months ago because the original finally died and everything has been fine. The whole problem started a few months ago when I didn’t drive it for a month and the battery was dead when I went to start it up so I just charged it with a car trickle charger to about 14 something volts then the car started fine. But now almost every time after I drive it like 30 miles or so when I turn the car off the battery loses charge or volts go down to like 11 or 10 almost right away and the car won't start. I had the battery tested and the alternator and he said they were good although he said the alternator and the battery were both putting out about 14 volts when the car was running and that seems odd doesn’t it? There is no corrosion around the terminals or wires!! What else should I look for? When the battery is charged or jumped the car starts fine!

One other thing I should mention is that sometimes when I pull out of my driveway in reverse then shift to drive the idle goes down and sometimes makes the car stall out. The volts go down when the idle goes down, not sure it that has anything to do with it.

If I was you, I would be looking at the ground connections but especially at the battery cable to starter connection. That connection tends to come lose and will cause problems like this. Its also possible that your battery was killed when it went to full dead as most batteries don't recover from that very well. When you said you had it tested, I'm hoping you meant it was load tested. If it passed a load test, then its probably Ok. Have you tested for something draining the battery? You'll need a DVM or VOM that can measure current and the knowledge to use it. If something is draining it, you'll need to start pulling fuses one at a time till you find the circuit that is causing it and go from there. Pull the codes too just in case.

It may sound simple, but my new Silverado came with a battery that had two bad cells in it. After a couple of months...same issues as you. The Stealership tested it and replaced battery and now no problems.

Dead cell?

Yes I also believe it is a dead cell.! Replace the battery,, the car is ok.

I am having similar issues as well. I am keeping my car in a storage container for the time being and after i accidentally left my radar plugged in and completely killed the battery I went and bought a new one. Drove the car for the day and then put it back into storage for a couple months (making sure nothing was left plugged in). Went to drive it a week ago and when I got in the car acted normal but when i turned the key it just clicked like a dead battery. Put the cables on it and it started just fine. Initially the volts inside the car were around 13.4 but as i drove it the volts slowly dropped to around 13 after around 30 minutes. After the drive I turned the car on and off 5 or 6 times and it started just fine. Since i had no time to work on it I just unhooked the battery for now and left it till next time. Any suggestions would help?

A lot of people seem to think that if everything is turned off, there is no battery drain. Unfortunately this is not the case. There is always a drain although it should be very small in the low milliamps, but it is always draining. You can't let it sit for months without re-charging or putting a battery tender on it. I remember a post in this forum too that a very knowledgeable person with batteries made a good case as to what happens when you drain even a brand new battery to zero... the thing is trashed permanently.
Drive your cars. Keep it charged up by whichever method you choose, driving it or battery tenders.

Thanks for the help guys I'll check it out today. I forgot to say the new battery is a AC Delco.