- May 6, 2011
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99 Chevy Cavalier. It has a 3 year old battery and a 9 month old alternator. Usually it starts and runs fine.
Since the car has no battery gauge, I placed a multimeter across the battery terminals. The battery voltage reads about 12.0V when off, 12.6V when idling, and about 13.5V when revving. All of this varies a bit depending on electrical load. Sounds about normal right?
At random times as soon as you start it, the meter reading rapidly drops to under 10V. The engine will stall if its not shut off. Revving the engine does not help. However, as soon as you shut it off, the meter returns to 12V. The car will usually restart without requiring a jump, if not left running in this "shorted out" state for too long. Then the next time you start it, everything will be normal. Then you shut it off and restart it and it might go below 10V. It seems completely random, although heat does seem to be a factor. The longer you allow the car to cool, the more likely it is that it will start normally.
Here is one other interesting piece of information. IF you start the car and the meter drops below 10V, all it takes is a quick jump to bring it up to 13V. I mean literally tap the jumper cables onto the battery terminals for one second and the meter jumps from <10V to 13V and everything seems to be normal.
The auto parts store checked the battery and said it is dead, it is at "65%", whatever that means. I've seen plenty of dead or dying batteries but I aint never seen one behave like this.
For it to drop below 10V so incredibly fast, it takes a 50+ amp load to do that. Maybe even >100 amps. I've driven for over 45 minutes on battery power alone; it takes a long time for a normal daytime load to drain a battery to the point where the car dies. But when its in this condition the car dies within 20 seconds. It sounds to me like a serious electrical problem, and I dont want to just start replacing everything if it is going to be some intermittent short somewhere that I wont discover until after I've spent $200 on parts I didnt really need to replace. Is a 65% battery really that dead, or does it still have a couple years left in it?
Since the car has no battery gauge, I placed a multimeter across the battery terminals. The battery voltage reads about 12.0V when off, 12.6V when idling, and about 13.5V when revving. All of this varies a bit depending on electrical load. Sounds about normal right?
At random times as soon as you start it, the meter reading rapidly drops to under 10V. The engine will stall if its not shut off. Revving the engine does not help. However, as soon as you shut it off, the meter returns to 12V. The car will usually restart without requiring a jump, if not left running in this "shorted out" state for too long. Then the next time you start it, everything will be normal. Then you shut it off and restart it and it might go below 10V. It seems completely random, although heat does seem to be a factor. The longer you allow the car to cool, the more likely it is that it will start normally.
Here is one other interesting piece of information. IF you start the car and the meter drops below 10V, all it takes is a quick jump to bring it up to 13V. I mean literally tap the jumper cables onto the battery terminals for one second and the meter jumps from <10V to 13V and everything seems to be normal.
The auto parts store checked the battery and said it is dead, it is at "65%", whatever that means. I've seen plenty of dead or dying batteries but I aint never seen one behave like this.
For it to drop below 10V so incredibly fast, it takes a 50+ amp load to do that. Maybe even >100 amps. I've driven for over 45 minutes on battery power alone; it takes a long time for a normal daytime load to drain a battery to the point where the car dies. But when its in this condition the car dies within 20 seconds. It sounds to me like a serious electrical problem, and I dont want to just start replacing everything if it is going to be some intermittent short somewhere that I wont discover until after I've spent $200 on parts I didnt really need to replace. Is a 65% battery really that dead, or does it still have a couple years left in it?
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