I have had an ongoing problem with my 98 C230 for the last 6 to 8 weeks. About two months ago my battery went dead. This was the original OEM battery, given I've only put 24,000 miles on the car in more than 3 years (mostly street driving, in heavy traffic) it didn't seem unusual to have a dead battery. I called AAA for a jump but noticed an odd glitch when I was driving home. When sitting idle at a light, the turn signal began to blink erratically (many times faster than normal). I replaced the OEM battery the following morning with a Duralast (The brand from a local auto parts chain). I noticed no problems once the battery was replaced. After two or three weeks with the new battery, I once again had the same glitch with the turn signal. The problem seemed to get worse over the following week. I was due for a regular service and told one of the service reps at my dealer of the problem. They had me come in and checked the voltage and the alternator and said everything seemed fine. We were unable to reproduce the problem at the dealership. Given that it was a 30 minute freeway drive to the dealer, the mechanic seemed to think it might be a bad battery that was charged by the drive. I've continued to have the problem off and on since then. I've never had any problem starting the car and the problem only seems to pop up when the car is idling. I've noticed that the overhead light also dims and Flickers at times when the car is idling. I've also noticed the LCD screen on the climate control seems to be malfunctioning at the same time. The only time the glitch posed any significant problem was one instance when the car stalled after I removed my cell phone charger from the cigarette lighter while I was waiting at a red light. The car started up again with no problem.
Today I searched the message boards to see if anybody had a similar problem. I didn't see any posts that matched my problem exactly. I did find some good diagnostic info that was helpful. I checked the voltage via the climate control LCD screen (Holding down "Reset" and pushing "+" till #24 appears). The voltage while the car was idling was around 13.5. I was unable to get the glitch to occur at that point (never seems to happen when you want it to). I went back to a nearby auto parts store and replaced the battery again, as a last ditch effort before I drop the car off at my dealer for a costly fishing expedition. I was in a hurry and didn't have time to allow them to test the old battery. After installing the battery, I checked the voltage numbers. 12.1 when the engine was off and 13.5 to 14 while the car was idling. I drove the car around for a bit and noticed no problem. I remember the last time I changed the battery I had no problems for several weeks. I suspect the same thing might happen this time around.
Does anybody have any idea what could be the cause of this glitch? In many of the posts I read ,when I performed a search, the "Overvoltage relay" was mentioned numerous time. Could this possibly be the problem? Or could it be something as simple as a defective battery or simply a poor brand? If there is a short or something draining the battery, I'd think it would give me problems when I start the car. There are no warning lights flashing on the dashboard and I checked all the fuses (I'm not even sure if that was necessary, but I was out of ideas).
Any info or advice will be appreciated. And sorry for the long winded post. I wanted to give as much info as possible given the vague symptoms I've experienced.