W211 battery totally dead after 7 days without use

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speedyyellow

Member
Joined
Jul 19, 2010
Messages
34
Location
Cambridgeshire
Car
W211 E500
A couple of weeks ago my wife came down to the car after work to find that it wouldn't unlock with the key fob, and if she used the physical key to open the door she couldn't start the car.

Now, I suspected the battery was on the way out as it had been labouring slightly on starting for a while, so thought I'd get it changed before winter arrives. I swapped out the main battery and the car sprang back into life and all was good again.

Fast forward to tonight and after returning from a week away the car was totally dead again. I'm assuming that there must be something that's draining the battery, but have no idea what this could be or how I go about figuring it out. Help?
 
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The 211 has a very complex electrical system. It is not unknown for the cables connecting the auxiliary battery to cause problems, or indeed the aux battery itself. It may prove cost-effective to get a mb indie to give it a going over, as guessing at it will probably prove expensive and unfruitful.
 
Under the pollen filter moulding, rear left side of engine compartment, behind the washer bottle filler. You need to remove the pollen filter cover to see it. It's small, more like an alarm system battery.
 
Does this car have Comand, if so ensure it is shutting down properly.
 
Nope, no comand fitted.

Ok, so first steps would be replace the aux battery, recharge the main one and see how I get on. Are the aux batteries easily obtainable? We're due to go away again this weekend so need to try and get something sorted ASAP.
 
Had a similar problem. Renewed main battery but after a couple of months same problem. It turned out the new battery was faulty and MB replaced it but only after a days testing
 

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