how can a battery have 12.8 volts and not even power a dome light? last night i ran the car for a few miles. today, dead batt.
i disconnect the batt and put on a digital voltmeter: 12.8 volts,
great. with the battery in the car, the dome lights were VERY dim.
Batt volts read about 10. disconnect the batt, volts go right back
up to 12.8!!
I jumped the batt with my truck. engine barely started then would die if i turned on ANY electrical accessory. even the brake
lights. Finally put a 'load tester' on the batt: FAIL
what looked like a massive current draw somewhere in the elec
system turned out to be a shorted cell in the batt. (full voltage
until a load)

lesson: I was ready to search out a gremlin, the tiniest short to
ground and got the sand whipped out of me by a bad batt.

sounds stupid, but thought I would remind everyone not to
'over-diagnose' but look to the simplest part of any system.

 

You got it. Many times when I reply I stress the importance of a good battery. In fact the dealer my wife uses for her Blazer(under warranty)automatically replaces the battery whenever they change an alt. Periodic trickle charging is a really good way to exxtend the life of your battery since an alt only will keep the battery at around 80% of capacity. As I have said more than once here my original battery from my 89 rock is still running a neighbors car. I trickled it once a month as long as it was in the car.