RED BATTERY DASH LIGHT
Thread Starter
Junior Member
Joined: Oct 2020
Posts: 31
Likes: 3
From: Central FL
C300 sport 4matic
RED BATTERY DASH LIGHT
I had the solid red battery come on while driving yesterday. I replace the only battery in my C300 (2011 sport 4matic) a few months ago at benz. Car drives ok, nothing odd to report other than. I know this light means charging system BUT using my DVOM I get 13.5 volts while running. I've replaced the belt and pullys recently a few months back also so slipping is not the issue. I brought it to my local auto parts store and alternator/voltage reg and battery all passed. Ive read that the ECM on top of engine could be bad and sending a false reading to voltage regulator or possibly the current indicator which is the little black box on negative battery cable located at battery could be the culprit and may need to replace whole cable as that is how its sold. Any info or way of diagnosing the problem would be of great help. I understand this is a question for the more knowledgeable group here. Thanks in advance.
Junior Member
Joined: Aug 2010
Posts: 47
Likes: 5
2008 C300
I had the solid red battery come on while driving yesterday. I replace the only battery in my C300 (2011 sport 4matic) a few months ago at benz. Car drives ok, nothing odd to report other than. I know this light means charging system BUT using my DVOM I get 13.5 volts while running. I've replaced the belt and pullys recently a few months back also so slipping is not the issue. I brought it to my local auto parts store and alternator/voltage reg and battery all passed. Ive read that the ECM on top of engine could be bad and sending a false reading to voltage regulator or possibly the current indicator which is the little black box on negative battery cable located at battery could be the culprit and may need to replace whole cable as that is how its sold. Any info or way of diagnosing the problem would be of great help. I understand this is a question for the more knowledgeable group here. Thanks in advance.
Senior Member
Joined: Apr 2014
Posts: 323
Likes: 34
From: Massachusetts
2010 C350 Sport
I had something similar happen about a month ago. While driving the red battery light came on so I went into the engineering menu but the onboard diagnostics showed everything was fine with voltage. Then a few days later the engine sounded like a washing machine full of rocks so I knew something with a bearing failed. Turns out it was the alternator.
I think the alternator was actually giving me issues for a few years. The car would feel like it misfired under heavy acceleration onto the highway and then go into limp mode.
Just like JimMBC300, once I replaced the alternator there were no more electrical issues.
I think the alternator was actually giving me issues for a few years. The car would feel like it misfired under heavy acceleration onto the highway and then go into limp mode.
Just like JimMBC300, once I replaced the alternator there were no more electrical issues.
