New battery or battery AND alternator ? - PeachParts Mercedes-Benz Forum

Andy_M · #1 03-14-2008, 08:11 AM

A couple of weeks ago while sitting in the car while it had been idleing for a while I noticed all the warning indicators start to glow, at first dimly then full on. I tapped on the accelerator and the lights went out and never came back on. This happened one other time about two weeks before that under the same circumstances.

Last night my wife had the car out on an errand about 40 mins away. On the way home, she noticed the ABS and SRS indicators about half way lit up, then they faded back off. Then, 4 or 5 miles later, the dash lights slowly started to dim. They kept dimming out slowly until they were almost off. The headlights had also dimmed. Then the car started to run rough. She feathered the gas and the car came back to life, the lights went back on full, and the car was fine. Maybe 5 mins later it did this again, then 2 or 3 mins later it repeated the process, but this time it went dead about a mile from home. She called and said it was absolutely dead. She had interior lights but got nothing if she turned the key. I went to where she was, took out the jumper cables, and asked her to try the key again. It turned over but would not start. I jump started the car and drove it home. It was fine.

Obviously the battery has been drained, but does it also sound like the alternator needs replacing ?

mbdoc · #2 03-14-2008, 08:15 AM

Most likely the alternator is the PROBLEM not the battery.

IF you are a DIYER you can try a voltage regulator first.

Andy_M · #3 03-14-2008, 08:28 AM

That's pretty much what I thought.

The battery does look fairly old and has been drained dead, so I'll probably just replace that too at this point. Better now than the coldest day next winter.