Today I topped off my ac freon and noticed that the electric fan was running more often than before. I drove to a neighboring town and back for errands which was around 60miles round trip. I got back, put the top up, and then the battery voltage warning light illuminates. I shut the car off and put the message center into the voltage display. I drove around and it stayed at 11.6-11.8v. I then drove back across town to go home a few hours later and the voltage stayed the same. It may have been 11.5 when I shut the car off, but on the trip it didn't go above 11.8 but fluctuated as I drove with the ac, headlights, and radio on. When running should the meter go up to 13+ when the alternator kicks in? The car is a 2006 CLK500 with 46k miles.

 

A properly functioning electrical system will have 126v at rest, no less than 11v during cranking, and 14v at idle.

 

A bad alternator will kill the battery, so my approach is to first change the battery, Measure the voltage at idle, and if it is below 14V change the alternator.

 

I charged the battery for an hour and a half, hooked it back up and the car read 12.1V. After starting it dropped to 10.4 or so and then came back to 11.7. I then drove to the battery parts store and he said the car was not charging. When I put it back in the garage the car was reading 11.5V. I guess it is time to order an alternator now? Is the voltage regulator built into the alternator? It's odd that the alternator is randomly shot at 46k miles.

 

How old is the battery?

 

I can't check because I am on vacation. Try to go to your Mercedes dealer and have them look it up using your VIN unless someone else jumps in with an answer.

 

The battery is an Everstart (which I'm skeptical about) that is marked 2015.

 

Ok. The culprit might not be the battery then. I asked because a typical battery would last 5 years. I changed the battery twice in the 13 years of ownership of my w209.