E350 Coupé 2010 red battery light

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New Member
May 4, 2020
United Kingdom
E350 Coupé 2010
Hi all, I have a 2010 E350 diesel coupe.
The red battery light comes on intermittently and sometimes shuts down command/radio.
I have looked at my onboard computerthat tells me the following:
Engine off-
Supply voltage of HU 12.3v
Battery voltage via CAN 12.3v
Engine running-
Supply voltage of HU 11.6v
Battery voltage via CAN 11.8v

Is this a battery issue? Main or auxiliary?
Is this an alternator issue possibly?
The car drives perfect and at this time the red battery light is intermittent. THANKS
Probably an alternator issue. It should be 14.4V running directly off the battery or the back of the alternator. It has smart charging so give it a minute or so running to check the alternator output.

Get a genuine alternator and you may need a new battery too. My advice is to buy genuine batteries, they are better.

We have had so many issues with aftermarket alternators on these engines.
I had the red battery light come on on my old E320 (W211 series so no stop/start) but otherwise same engine.

Local Indie diagnosed as alternator failure (££ Ouch) which I had replaced. If that is the problem after replacing the alternator I'd recommend charging both batteries to 100% with a good quality smart charger. That way you start from a known position.

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