W203 Battery Alternator red warning

[mejermy]

However the battery is showing 13.3 V key off, and 14.1 when running, warm after a half hour drive, which suggests it's in good order and the alternator is charging doesn't it?

Any suggestions welcome. Loth to go scratching about underneath in this weather to remove the alternator, esp since the charge rate seems reasonable.

 

[Ted]

The alternator not only charges your battery, it also contains circuitry to turn off your warning light.
Your voltages seem reasonable, but the alternator may only be putting out a percentage of the potential current, the only way of really knowing is to get the charging checked out by a reputable auto electrician.
Wiring to an alternator is usually fairly simple, so I'm afraid it looks like your alternator may be on its way out.
One question, does the light come on with ignition on, and stay on, or NOT come on with the ignition, and then glow with the engine running?

 

[mejermy]

Thanks for the reply Ted. It's my son's car, so I only saw the fault briefly when he shot up early this morning for me to check it out. The warning isn't the small rectangular tell-tale which comes on with the ignition and extinguishes when started, as on all(?) MBs. It's a text on the computer message window in the centre of the panel where the OAT/consumption/kph etc is also displayed depending on your selection through the wheel buttons.
When I switched it on this morning the message appeared within a couple of seconds.
Yes; I fear it may be a visit to an auto electrician, but hoping to avoid that.

 

[mejermy]

I'm reminded by a post on the other side 'Many messages can come and go on all Mercedes never to be seen again' to update this thread. As soon as the weather warmed up a bit the message ceased to appear. Suspect it's just a tired battery stretched by the low temps. Prob original equipment (2005, 130k miles car).