mgdad

I will be leaving my 2004 E500 for 6 weeks in my driveway in cold winter conditions. Last time I did this for 4 weeks I came back to a completely dead battery, requiring key entry to the trunk. I now have a trickle charger and am wondering what I need to do. Should I just attach the trickle charger to the main battery in the trunk while I am away, or should I disconnect it and keep it inside perhaps? What about the smaller aux battery under the hood?

kajtek1

Strange. We had W210 and W163 sitting in carports for 5 weeks and they always started on their own power.
W211 has more electric gadgets, but sleep mode on new electronics is expected to be more efficient than on older one. Maybe your difference was current leaks due to moisture in cold weather?
So first check if you car goes into sleep, the cluster and light go off in 10 or 20 seconds.
Now the best protection for battery is just pulling the clamp off.
I did it in July on 2 of my MB and reconnected after 2 months with no problem. W212 even hold garage door codes in memory.

rapidoxidation

If you already have the trickle charger, connect it and forget it. The cord (similar to a lamp cord, yes?) will easily go through the trunk weatherstrip.

kajtek1

Trickle charger is design for overnight boost. Left for long time it can boil the battery dry, not to mention what high voltage can do to car electronics.
For prolonged battery keeping, I mean over 6 months the battery maintainers are recommended, still with advise to disconnect them from the car as a precaution.
All in this life can fail and you don't want to trigger chain reaction if you can easy avoid it.

rapidoxidation

I should've been more specific: Battery tender. Designed for keeping a battery in storage but charged for extended lengths of time.