Just helped my neighbor's friend jump her truck.
So gather around for this tale of woe. She brought her truck in - they said the battery was bad and replaced it.
It died today at the convenience store down the street. They called us and we headed over.
While jumping it, I noticed the positive battery terminal was so loose that I could pull it off. Truck did run with the battery cable off, which is a good sign.
We swung by our house and I tightened down the battery cable. Just for ***** and giggles, I checked with a multimeter while the truck was running - about 11 1/2 volts. When we turned the truck off, we were getting a little over 9V off the battery. Same voltage on the back of the alternator terminal as well, so the cabling was fine.
Truck wouldn't start again, obviously. Pulled the car around, and I checked my multimeter against the car - a healthy 14V.
Now I'm not a mechanic, but that sure seems to indicate a charging problem to me - the system isn't producing enough voltage to keep the battery charged, but has enough voltage to keep it running (at least for a bit).
As a bonus, she's having trouble finding someone to work on her truck since it's a '94 and that's "too old" for many mechanics. Not sure what that means, unless modern mechanics are only learning how to read OBD II trouble codes.