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Just bought a 2 year old E class diesel estate 2.0 e220d. Whilst sitting in my drive, learning all the new shiny buttons and updating the maps etc, I got a message "12V Battery See owners manual" and an email from Mercedes Me saying "the starter battery charge status of the vehicle KR21CXC is critical". I started the engine and let it run for a bit. Later I measured the battery voltage using my multimeter (in situ, but with the ignition off) and it read 11.6 volts. Took it to MB and they "checked" the battery and said it was fine, just needed charging. I have since driven it some long distances (600 miles), but when I use the dashboard display to read the battery voltage before starting the car it generally reads 11.8 volts, which still seems low to me. It rises to 14.8 when I start the car, so the Alternator is working fine.<br />
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I realise that ideally I should disconnect the battery and measure the voltage without the current drain to get a proper reading, but just wondered if those of you who have the ability to read the battery voltage on your dashboard before starting the car also experience the same sort of reading, i.e. 11.8 volts?<br />
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Thanks, Anthony
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What you have experienced is normal, the 12v battery gets drained while you're sitting in the car playing with the gadgets.<br />
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At 11.8v, you'll need to take the car for a long drive, or use a trickle charger, e.g. CTEK.<br />
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If charging the battery while driving the car, note that the alternator will show 14.3-14.8v when the battery is below 80% capacity, after that the battery management module will reduce the charge level and the alternator voltage will drop to 13.3-13.7v. At this point, the battery is being trickle-charged by the alternator until it reaches 100% capacity (in order to prevent battery damage). If you don't see the alternator voltage drop, then the battery is still below 80% capacity.<br />
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If the battery voltage remains low even after a long drive, then Your battery is probably tired, but even so it will still start the car for a long time, months or even years. The first sign of trouble will be when Stop/Start no longer works.<br />
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But, again, most likely all the car needs is a good long drive to fully charge the battery.</div>
