I have a 1995 C220 Elegance. I'm based in the UK. Car is parked outside, 650 feet up a hill, quite exposed.

My battery always goes flat, especially in frosty/cold overnight conditions.
I'm sure this has been happening ever since I bought the car from new. New battery fitted after about 4 years, MB said that the car had so many computers that this would flatten the battery.

I've just replaced the battery again and after only 2 months, it is needing a charge and the car failed to start on 2 occassions last week. During this time, the car was parked overnight without the alarm turned on. Twice, when I tried to start the car, it failed and straight away, the alarm went off. I had to remove the battery terminal to stop it. I leave it on a MB trickle charger overnight but I suspect that either the alternator has stopped working properly or that something is flattening the battery overnight or both. A garage tested the alternator and said that at 2,000 rpm with headlights on, it was producing about 13.5V. 90% of my driving is done at below 2,000 rpm down country lanes. I tested the battery last night and it was showing 13 volts, I plugged in the trickle charger and this morning it was at about 11 volts. I'm wondering if it is possible that the heated wing mirrors can come on even when the ignition is off. I've begun "feeling" the wing mirrors before and during starting the car. I've found that they are quite often very warm for up to 5 minutes after starting the car.

Is this normal.?
Can they come on when the ignition is turned off?
How can I isolate them to test my theory, I cannot find a fuse for them?

Getting very desperate now, I know that if/when I leave the car when I go on holiday that the battery will be flat when I return.

Hope someone can help.

Cheers
Dave