Battery Drain

I have had batteries and alternators pass Canadian Tire (the Canadian version to your AutoZone) tests, and still not be any good. I replaced them, and the car worked fine. The last time I took in a batter it was because my '96 Bonneville was doing the same thing your Blazer is doing. Canadian Tire said the battery was fine. I said, to hell with them and bought a new one anyhow. The car runs perfect now.

Not everything is on your normal fuses. You said you checked shutoff current drain but you didnt tell us what it is.

Take off one of the battery cable terminals, measure the current draw while the key is off by inserting an ammeter in between battery post and its unconnected cable.

You may have to wait until some of the electronic control modules go dormant. How much current do you read? It should be no more than about 150 milliamperes max.

******Let us know the reading, and we will go from there.******

Common problems include courtesy lights that are not shutting off. A 10 watt courtesy bulb would draw about 700-750 ma, and that will run your battery down pretty quickly.

It is certainly not impossible that you did some damage to the system when you gave your friend a 'jump'. Done correctly, it usually goes fine, but if you don't do it right, you can damage diodes, etc.

In your description of the problem you said,

From that statement I assume that you mean the current draw from the battery is something greater than zero when everything is turned off and the alternator is connected. Then when you disconnect the alternator, the current draw goes to zero. If true, you have a bad alternator (diode) no matter what AutoZone says. Charge the battery (important), change the alternator, and your problem will go way.

I have personally seen my Alternators, Batteries, and Starters pass Autozone's tests and they were actually bad. I have actually had to walk some of their personnel through the test because they didn't know how to do it. (Not all stores apply to this). Try to find some local auto shops that will do the testing for a minimal, or no charge. ex: Pep Boys, Checkers, and Napa too. Have it tested at different places. I went out and bought myself a cheap tester and it has been right everytime.

This is an alternator problem one of the positive rectifier diodes is shorted allowing current to flow both ways . This sometimes happens when an vehicle is jump started, an high voltage surge to a dead battery through the alternator usually blows an weakened diode. The testers mentioned sometimes miss the problem. I have seen this fairly often. I repaired alternators for an living.

Rey

Rey

I question the validity of a " Twilight Zone " test. Sure, they can hook it up to a spinner, and see if it puts out juice. By your own investigating, current draw drops to zero when alt. is unplugged means the unit draws current. How about having a rebuilt / and your alt. checked with a VOM for resistance from case to output terminal. A bad [ shorted ] diode will allow current flow from term to case.

Thank you all for your post, you've been a ton of help. I've been busy and haven't gotten to check out any of your suggestions. I think I'll try 451CTDS's suggestion and test the resistance. If no luck, I'll bring it somewhere else and have the alternator tested. I just wish they'd let me return the alternator if that's not the problem, but that's not the case.

snipped-for-privacy@nospam.nix: I think it's drawing around 300 ma. But as much as

900, it changed on me (probably something to do with leveling out after the battery was disconnected) Thanks again, I'll post again when I have more info.

300 to 900 milliamperes is too much, as you have already found out. If that drain drops to 100 or less when you disconnect the alternator, then you are on the right track.

I have a similar "problem" with my Buick Park Avenue and I'm wondering if it's my alternator. Before getting a new battery, my car started up fine but the volt indicator went down quite a bit and then it started rapidly going between

12.1 volts to 12.9. I took the car to Canadian Tire and they said my battery was good. I then took it to a GM dealer and they said the battery had a bad cell and my alternator was good. I got a new battery and now the car starts at 13.9/14 and it goes down to 12.8 unless, I'm driving up hills than it dips back up to 13.1 to 13.3. The reading doesn't jump around quickly, or as low, like it did with the last battery. It will settle into the 12.8 range and stay there, except for hills. However, the other day, it did go down to 12.5 volts, which I've never seen it go that low with the new battery but it didn't stay there very long. I have no doubt the last battery had a bad cell since the new one does perform better but I'm wondering if there might be something wrong with the alternator as well, even though it checked out fine. It seems weird that my car starts around the 14 range and drops, considerably, as it starts warming up. With both batteries, particularly the old one, my car does have a weaker engine idle sound when left for a couple days. But it always starts up fine and in the normal volt range.

Jeff