W211 E320 Battery Warning Light

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jshodgson

Active Member
Joined
Aug 25, 2017
Messages
138
Location
Torquay UK
Car
E class 320 cdi sport 2007
For the first time ever I got a red warning light (battery symbol only- no words) when I got back to my car after work. It started and ran fine.
Next day I did a 160 journey and again the warning came on as soon as I started, went off and kept on reappearing throughout the journey. When I got home I checked the battery voltage and it said 12.0v.
Next day I checked the voltage and it was 11.5v.
Car started fine and ran normal, again with the warning appearing now and again so I drove it with the battery voltage displayed and as soon as I started the engine it went up to 14v, when I stopped the engine 12v. I then charged the battery for 3 hours and got the same reading (12v and then on start up 14v and then when the engine is off 12v).
I checked for a second battery in the engine bay but couldn't find one so I think I just have the massive one in the boot.
Could it be a failing battery? Alternator (although it looks like it is charging when I am driving) or could it be something else?
 
Probably a duff cell or two in the battery - how old is it?
 
If its the original battery on a 2007 build it may well be reaching the end of its life.
 
It has an MB sticker but looks great although I’m not used to seeing old batteries outside of the engine bay.

Can I take it out and stick in a new one or will I lose radio code and run into other problems?
 
If MB stickered then probably is its original. Would expect it to look clean - they are not in a particularly dirty environment.
If you remove and replace then you will have to re-learn things such as windows and sunroof. Not sure re radio codes as not changed battery on my 211, but that may need doing too.
I understand that the MB batteries are Vargas so look for those - not forgetting to check price with local MB dealership as surprisingly they have been known to be quite reasonable in price and you should get them to fit for the price.
 
When I replaced both the battery's on mine there wasn't any radio codes to put in just cycle the windows and sunroof so the auto function works that's all. Not got a diesel but I can imagine the main electrical system being the same ish.
 
STAR diagnosed a faulty alternator. Going in Thursday to be replaced.
 
Alternator looks like it failed as there was a split in the inter cooler pipe above it. Both now replaced.
 

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