I have W211 Mercedes E270 CDI. If I do not start the engine for more than about a day, battery becomes completely empty. I first thought the battery completed his life and is dead. So change it with brand new one but it did not solve the problem. If I start the engine every day, I sometimes see “Malfunction electrical consumers switched off” message along with a battery symbol on the display. I get checked the alternator. It recharges the battery well. Any idea the possible problem?

 

Sounds like what's called a "deep discharge" due to a grounding problem. Based upon your description I would take the car to an independent auto electrical shop and see if they can find the short.

 

Do you mean you get the red warning if you don't drive the car for a day or is the battery really flat and the car does not start either? If it did start, it could be the AUX battery. If it does not start and the main battery is good and the alternator is good, there must be a huge quiescent current that should be easy to measure.

 

Thanks for your reply.

Car doesn't start. Battery is completely empty. I need to recharge battery externally or by mounting to another car's battery to start the engine.