Battery drain on startup issue

[tetstb]

I'm looking for some help/advice please regarding my 2006 CD220i estate auto which has a strange problem of draining the battery dead on start sometimes.

The batter can be fully charged having either jumped the car or charged overnight on a charger and when attempting to start the starter engages , electrics wake up and then it shows signs of a flat battery.

The battery has been tested and the alternator has been checked to ensure the battery charges correctly and there are no shorts, normal light drain for the radio etc is show at idle.

An auto electrician has looked at it and he says its a common issue and is caused by a fault in the heating system pre-heat and he says the heater is coming on and drawing 26 amps at start and this is killing the battery stone dead preventing it from charging.

He says it can be easilly disconnected but I thought I'd check.

Any ideas ?

 

[E270 Owner]

Surely you would get the auto electrician to disconnect it to test his diagnosis ?

 

[clk55M]

doesn't look like root cause has been identified. Might be a short circuit relating to the alarm? Had this in a past car.

 

[mersum1es]

If it's 26A draining current, there are not many places... something must be warm there (sounds like coolant heater)!

 

[tetstb]

If it's 26A draining current, there are not many places... something must be warm there (sounds like coolant heater)!

The theory of the electrician was that it was the coolant heater that was at fault, just wondered if anyone else had same issue.

 

[mersum1es]

The theory of the electrician was that it was the coolant heater that was at fault, just wondered if anyone else had same issue.

That's a pretty common issue in W203 and W210...

 

[tetstb]

That's a pretty common issue in W203 and W210...

Thanks