I recharged the battery on the slow charge 2 days ago and yesterday when I put the battery in the car, the car started like a charm. I drove teh car yesterday and made a few stops and had no problems. This morning I turned the car on and it started like a charm once again. I drove around all day today and had no issues. I go home feeling good thinking maybe the car is fine now. Maybe it was the voltage regulator that was the problem. No chance of that . An hour and a half later, I tried to close the widows in the car and it was dead again . I'm wondering how the battery could have that quickly?

__________________
1989 300CE Astralsilber/Schwarz
1992 300CE Schwarz/Schwarz

I would suggest getting a volt meter hooked to a cigarette lighter adapter so that you can monitor the voltage as you drive. Should be around 13.5V with the engine running. If the voltage is good, try disconnecting the battery each night. If it holds a charge then the problem is likely a voltage drain.

One trick that has worked for me in the past for isolating a battery drain is to remove one fuse at a time in the dark. I was able to locate the offending circuit by seeing a small spark jump the gap at the fuse as I removed it.
Worth a try

lino,I am no mechanic but what happened to me was the negative terminal of the alternator was loose last winter in minus 20 celsius.It died once.
I tightened that and the car seems okay now.

__________________
Tom 2010 C250 4-matic Sport (Canada)

I had a weak battery once and the symtoms are exactly like yours. There was a weak/shorted cell and although it puts out the 12+ volts with a voltmeter the weak cell dies very quickly and intermittently, ie. overnight and with the stereo on while you fiddle away or no reason at all. It drops one cell down (2V) to 10+V and you will not be able to start the car. Doing a load test on the battery will show up this problem. When you are bench charging, this cell will show up as the one that doesn't bubble the same with the rest.

__________________
1992 124 E200 (Euro)

Very good advice. Mine needed to be tightened once before too. Now they are quite tight though.

__________________
1989 300CE Astralsilber/Schwarz
1992 300CE Schwarz/Schwarz

Thanks for the advice. My mechanic checked the fuses one by one and couldn't see a problem. I may have to try disconceting the battery at night and see what happens. The car is dead now so I have to charge the battery tomorrow.

__________________
1989 300CE Astralsilber/Schwarz
1992 300CE Schwarz/Schwarz

the voltmeter is a good idea, I believe JEGS sells one that plugs into the cig lighter.

__________________
2005 Mercedes C230k sport sedan, 6 speed
1987 Porsche 924S - 968-engined track car

I found one thing that is causing a drain finally!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Today, when I installed my new 150 amp alternator ( go to this thread for more info: http://www.peachparts.com/shopforum/showthread.php?t=123957). One of the wires on the positive terminal was found to be draining the battery. It is either for the alarm system or the PIAA fog lights that used to be in the car when the previous owner had it. I tookthe wire off off the battery terminal and covered it up with some electrical tape for now.




Now it's time to find out what exactly that wire does.

Attached Thumbnails

 

__________________
1989 300CE Astralsilber/Schwarz
1992 300CE Schwarz/Schwarz