Re: battery drainer? - Saab General Bulletin Board -

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Re: battery drainer?
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Posted by Ari [Email] (more from Ari) on Mon, 20 Apr 2009 03:51:26 Share Post by Email
In Reply to: battery drainer?, Ellie, Sun, 19 Apr 2009 19:27:38
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A normally operating alarm won't drain the battery overnight.

Occasionally the trunk light will get put into the mode where it is on all the time, and as others have noted, stuck brake lights. If the trunk light isn't on, and you don't notice the car giving off a nice red glow at night when it is turned off, it isn't a stuck light.

While I've seen cases where there is a sneak battery drain, these are very few and far between. That doesn't keep folks from going through all sorts of tests to try and find them. Stick with the most likely problems first.

Yes, you could have a bad alternator. If the alternator isn't charging the battery well, the battery will die. Turn the key to ON, but don't start the car - you should see a Battery light. If you don't, there is a problem with the charging system. The battery light should go out when you start the car, but if you don't check that the light comes ON, you can have a problem in that wiring and indication system. Even if the wiring is OK, the alternator might be getting tired. Put a voltmeter across the battery terminals and start the car. Even at idle, you should be seeing at least 13.0 volts (normal is 13.0 to 14.4 or so). Turn on the headlights and set the cabin fan to HI. The voltage should drop down, but no lower than about 12.8 volts. You could have a bad voltage regualtor. The alternator rarely fails, but the VR can. The VR can be replaced without replacing the alternator - a much cheaper solution.

Your new battery has gone flat a few times. That's not good. Car batteries aren't designed to be fully discharged. Every time they get fully discharged, they lose some life. A brand new battery can be destroyed with just a few full discharges. You can charge it, but it can go flat overnight. So it is possible you got a defective battery, but more likly you've got a charging problem, which killed your first battery, and is now killing your new battery.

If you don't have a voltmeter or aren't comfortable with doing this sort of testing, bring the car to a place where they can load test the alternator with it in the car. If the alternator fails the load test, see about having the voltage regulator replaced. If they want to replace the alternator (not cheap), ask them why the alternator needs replacement when it is likely just the VR. There are cases where the alternator could need replacement, but again, they should provide a good reason.

But flat batteries are usually due to bad batteries and poor charging. It is rare that it is due to some unexpected current drain. It does happen, but it's the last place to look, after you've ruled out the charging system and the storage system (battery.)

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