bascule Posted February 15, 2006 Share Posted February 15, 2006 About a month ago I left the dome light on in my car. The next morning my battery was dead. I got my roommate to jumpstart my car, and it's been working ever since, but it's been sluggish to turn the engine over. As time wore on, it seemed to do worse and worse, with the starter motor struggling more and more to get the engine to turn over. Last week, in bitter cold the day after it snowed, my car simply would not start. I got it jump started again, and drove home, and had the same sluggish engine turnover problems that I had before. I was certain I needed a new battery. Monday morning, again my car would not start. So I rode my bike to work, and did this again yesterday, having failed to go get a new battery on monday night. So I got my roommate to jumpstart my car again... Except, whoops, I hooked my battery up to my roommate's truck in reverse polarity! The jumper cables shot off huge sparks when I hooked them up, which was my first clue something wasn't right. I opened my car door and noticed the dome light wasn't on. I put the key in the ignition and tried to start my car, finding it completely dead. I guessed then that the polarity was incorrect. A small amount of smoke was visible in the area directly in front of my battery. I unhooked the cables, reversed the polarity, and my dome light came on. My car started just fine. I thank my roommate and took off for an auto parts store. I drove up to the door, saw there was an open sign in the window, and shut off my car then got out. However, when I went up to the door it was locked. Dread crept through me... I had foolishly left both my jacket and my cell phone at home, and it was starting to snow. After seeing the small amount of smoke rising off my battery, I was certain it was destroyed. I got into my car fearing the worst, and attempted to start it. Much to my surprise, not only did the engine turn over, but turned over rapidly without struggle just as it had before I had left my dome light on and apparently damaged the battery. I drove to another auto parts store which did turn out to be open, and spent about 20 minutes trying to pick out the correct model of battery for my car. I noticed they charge an extra $20 if you don't exchange your old battery for the new one, and I didn't really want to have to stand out in the snow without a coat removing my current battery just to save $20. I decided to see if my car would start again. Just like before it started instantly as if my battery were completely aproblematic. I decided I'd just see if my battery continued to perform like this, and drove home without replacing it. This morning the ground was covered with a thick blanked of snow, and once again it was bitterly cold and snowing just like the night when my car would not start before. I hopped in my car fearing the worse, but once again my engine turned over without a struggle. This is the first night my car has lasted after getting jumped when I got in in the morning and it started without struggle. Somehow, hooking up my battery to my friend's truck with reverse polarity fixed it. I asked an electrical engineer friend of mine about it and he said he was surprised the battery didn't explode. What did I do? Why did this seem to fix my battery? Link to comment Share on other sites More sharing options...
woelen Posted February 15, 2006 Share Posted February 15, 2006 Probably the short circuit current has removed a bad contact. It is a fairly well known thing that bad contacts with a large contact resistance become very hot with large currents. With these large currents, the contacts can somewhat melt together and then the resistance drops considerably. Link to comment Share on other sites More sharing options...
insane_alien Posted February 15, 2006 Share Posted February 15, 2006 hmm... maybe the plates were picking up impurities(not unlike how a catalytic converter can be poisoned) and the reversed polarity electrolysed the impurities off. i would still suggest a new battery. EDIT: actually woelens response seems more probable. didn't see his post there Link to comment Share on other sites More sharing options...
YT2095 Posted February 16, 2006 Share Posted February 16, 2006 other than the 2 above, the shock of such brutality probably taught it a lesson in manners Link to comment Share on other sites More sharing options...
bascule Posted February 16, 2006 Author Share Posted February 16, 2006 Well, my battery is still hosed. I got up this morning to a snow-blanketed car and it was about -13C out. That was more than enough to ensure that my car didn't start. So, now I have a brand new battery and things are much better again. Link to comment Share on other sites More sharing options...
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