[aqua2006]

The red battery light came on while driving today on my 2011 C300. Made it home and looked the issue.
Measured the battery while engine on and it was 12.76 volts and does look like it was charging. The alternator is most likely need replacing? Please advise.

 

[JeffreyG]

How old is your battery? If it is original to car (12 years old) then I would look to your battery first.

 

[aqua2006]

Bought the car a few months back and looks like battery is not original but fairly new.

 

[rawill1164]

12.6v is barely enough with an engine running.
If charged it should be on float over 13.2v.

Should be a date stamp on the battery.
That said, it does not tell you how the battery has been "treated".

If it has gone completely flat a time or two it could damaged.

 

[aqua2006]

Replaced the battery and red light came back on so it's most likely alternator bad.
on ordered. Thanks.

 

[aqua2006]

Replaced the battery and red light came back on so it's most likely alternator bad. on ordered. Thanks.

Alternator was replaced few weeks ago so it's all good now. Also replaced upper/lower pulley and serpentine belt. Noticed today the temperature gauge was fluctuating at 80 and 85. Thermostat going bad?