QuestionMike
I have a 2000 Saturn Sl-1.The other day when I went to start it, inexplicably, I found the battery was dead. I later realized I had accidentally left the overhead inside light on over night. My plan then was to jump - start it with my wife's car, and then drive it around five or ten miles to charge the battery up enough so I could start it on my own the next time. Out of curiosity, I thought I would check with All Experts, and see just how far I would need to drive to minimally - ie, enough to start it up again - as well as to fully recharge it, as well as to ask how damaging such a strategy might be to an otherwise OK battery, and if an alternative strategy would be better. I happened on your reply 11/20/09 to "Mike". I was rather alarmed at your statement that "An alternator will not charge a dead battery, - ". Surely there are hundreds of people every day that have to get "jumped" to start, and who then drive for a while, get where they're going, and are able to start right up next time without having to go to the repair shop first. If the battery isn't being recharged, why does the car start the next time? Now in Mike's case, you felt the pothole had probably compromised his battery, and that could in turn have led to the charging system being compromised as it tried to recharge the damaged battery. Since there was no damaging event in my case - just my stupidity in leaving that light on - and no other reason to think there was anything wrong with my electrical system and 2.5 yr old battery, wouldn't my drive around strategy be OK?
Also, you said - in part - "and an automotive battery that is completely run down will fail if it is done more than a couple of times". If WHAT is done more than a couple of times?
Thanks for your help.
DBRJ
Answer If a battery is COMPLETELY discharged more than a couple of times it will fail. Starting batteries just aren't designed to do this. There are batteries that are designed for this duty, called "deep cycle" batteries. It is doubtful that your battery is completely discharged, and driving the car after jumping will probably bring it back up to charge. But, if it doesn't, you'll know why. Did you damage the battery? Some, probably. It really isn't worth worrying about, though. If the battery comes back up to charge from driving it, then it could last several years or fail next week. But, that could happen even if you hadn't run it down. The biggest problem with newer cars and their batteries is that the computer requires a minimum voltage in order to work. If the voltage is very low, the car may not even run. Again, it is doubtful that leaving that light on did that much damage. Be careful that you jump the car correctly, reversed polarity can and will fry the computer. There's nothing scary here, just some common sense and a little bit of careful attention to what you're doing. A good battery should last a minimum of four years; I once had a Delco OE battery in an Oldsmobile that almost made it to eight.
