Battery drain on w201 2.0 auto

[Sidhu]

The battery is draining on my car over night. I can jump start it and take it for a good 20 mile drive. It seems ok straight after I take it for a drive. Come back in the morning and it's completely flat not even a light on the dash. I've had the alternator tested and it's not fully charging but surely it wouldn't drain as quickly as it is. The car also has a new Bosch battery which is less than a year old. Thanks in advance for your help.

 

[paul_f]

It could be a drain or it could be the battery just isn't getting fully charged.

DO you have a multimeter with current setting?

One thing to try without a multimeter would be to fully charge the battery overnight - a 20 mile drive isn't enough to fully charge the battery especially if your alternator isn't at its best.

 

[190]

I agree that a 20 mile drive isn't going to remotely fully charge the battery so it's in an unknown state when you park it up. If you drove for something like 6 hours then maybe it would get there. As that's impractical and given it's a nearly new battery you really need to fully charge it properly with a battery charger before too much damage is done. Then monitor the quiescent current draw with an ammeter. As a reference point the current draw on my 1989 W201 was 15mA alarm off and 35mA with the alarm on. If you don't have an alarm then there is only the clock current which averages 5mA although you may see it fluctuate.

 

[a111r]

Could it have a faulty alarm siren, board damaged by corroded internal batteries?

If one's fitted it's likely to be behind the osf arch liner.