Dead Battery

[Marc]

I have an interesting situation with an 83' 500sl. The car normaly starts right up no problem. Last friday I took the car for a short errand, (about 5 miles) when returning to the car the battery was dead. I jumped it, drove it the 5 miles home, turned it off, battery dead. I stuck it on a 2amp trickle charge overnight and it started fine the next day. I put a multimeter on the battery with the car turned off and it read about 12.7 then started the car and it went to about 13.5 maybe 13.6 at idle, revving the car to 2000 or 2500 had no affect at all. We don't drive this car alot but I took it out each day since just to make sure it would start. Everything is fine. Then yesterday I remembered that a couple of days before this incident I had driven the car at night, so last night I took the car for about a 20 minute ride with the lights on, got back home, turned it off, Bingo! the battery is dead. Now first, I've only had the car about six months but the battery looks new, the lights do not get brighter when the accelerator is depressed so, that along with the reading on the multimeter, is the charging system working? If not would it be voltage regulator or alternator? Now I'm concerned that I may have a larger problem in that I think it unusual that the headlights would discharge the battery in that short of period with the car running and producing 13.5 - 13.6 volts.

Any comments or suggestions would be greatly appreciated.

BTW, charged the battery again and it starts right up. Maybe I should just tape a good flashlight to the hood for night time excursions.