Non Jeep car problem

[MIJeep]

I've got a 2001 Pontiac Montana with the 3400 V6 in it....here's the history.

When we got back to Toronto from vacation we went to get the van and it was dead....I assumed it was because we left the satellite radio plugged in and a week without being started made the battery drain. Got it jumped and drove from Toronto back to Battle Creek with no problems, shut it off a couple times for gas and food and didn't have a problem.

After getting home the van sat again for 2 days before being started, dead again...jumped it again and it was good to go. We've driven it every day since then and no problems till today. The van wasn't driven yesterday so it went from Wednesday night till friday morning and wouldn't start this morning.

I checked alternator output....14.5 volts

I've checked batt voltage a couple hours after shutting off and it was 12.something.

I was beginning to thing I had a bad cell and the battery just isn't holding a charge for more than a few hours before it drains.
Here's the kicker....I just went out to look into how to pull out the battery(it's mounted under the fuse box) and it started right up no problems. I kinda think it could be shorting to ground but why would jumpstarting the engine fix the short problem? I know I should check batt voltage when it fails to start but it always seems to happen during inopertune times like when I'm already at work and the wife is trying to leave for work.

Also, I know how to detect a short but I really don't know where to look for it on a car. What are some problem areas?

[MIJeep]

I guess I never really asked.......What do you guys think

Bad battery or intermittent short?

[b1pig]

it could be either one.

early GM alternators could have a diode go bad in the regulator. the alternator would charge and once shut off, it would discharge the battery.

a dead cell is also another option. you can usually drop it at a store (that provides this service.. often free) and they will charge it up and then load test the battery for you. If the battery is more than 3 years old, then i would lean towards the dead battery idea, myself... but no guarantee.

the other option is to disconnect the positive terminal on the battery. (engine off) run a multimeter between the positive terminal and the positive lead. start pulling fuses and see if the current draw drops. that is one way of determining what is drawing down the battery.

one problem for you... the location of the battery.

[MIJeep]

yeah, the location sucks....talking to guys at work today the concesus seems to be that it could be shorted internally in the battery which is why it wouldn't turn over like it was dead but then start no problem 4 hours later.

I'm sure the battery is more than 3 years old so I'm gonna change that first, not a bad idea to have a new battery in anyway. Maybe if I can get it out fairly easy I'll get it checked out first....I really hope it's not a diode in the alternator that doesn't look fun at all.

[b1pig]

a battery with a dead cell will do that. the one dead cell will allow the others to charge to near full capacity, but when turned off, that dead cell will actually discharge the battery. seen it in the Army where we tested each battery cell by cell. there are 6 12v batteries on every M-1 Abrams tank. :eek: