Flat battery W202 C220 CDI Estate

[oulrichs]

I've got a recurring issue which is driving me nuts with a current leak somewhere intermittently draining the car battery. Basically, I believe the normal current drain when the car is sitting locked and alarmed is in the region of 100mA? As far as I can measure mine is closer to 300mA (placing my multimeter between the battery positive terminal and the clamp) so if I leave the car sitting for a week or so the chances are it ain't gonna start, particularly in cold weather. With a handy 5 pound fuse adapter for my multimeter (from Maplin) I've measured all the circuits in the front and rear fuse box. All looks good apart from fuse 41 in the front and fuse 3,5 and 7 in the rear. 41 in the front has a 100-150mA drain. 3, 5 and 7 in the rear are all round 5-70 mA. Has anyone had a similar problem or any thoughts of what the problem could be?

 

[television]

Could you please put up the next 3 numbers after 202

 

[oulrichs]

The full chassis number is WDB2021932F9755701 if that helps. It's basically the last W202 CDI estate model (produced from late 1999 into 2000). It's got all the CAN network stuff - I've read some posts higlighting problems with signal aqusition modules etc.

 

[Ellsy Tanners]

You should always measure/check battery drain with the negative terminal of the battery, i dont know what difference this will make but its worth mentioning.

300 ma (0.03amps) is not exceptionally high, a 75 to 100 amp hour battery should last serveral weeks with that drain.

What is the capacity of your battery and is it in good nick?

 

[oulrichs]

Argghhhh, another morning with starting problems. My battery is a 100Ah Bosch - about 9 months old. Definetly agree with the advice to perform current measurement on the negative terminal. Shouldn't make any difference to the measurements but it's safer - no chance of fireworks or broken instruments if you accidentally short the disconnected terminal or meter-probes against the chassis. 300mA = 0.3A though, which means over 100 hours your battery is down by 30Ah. Also a good chill can easy take 30% off your battery capacity. I think it's these 2 factors that's killing me at this time of year.......

 

[television]

The max drain on any car once its gone to sleep is 45ma.
300ma is way over the top, and that is 8 amps per day

 

[oulrichs]

I disconnected the control units in the 2 rear doors about 2 months ago. It still seems to draw aroun 80mA after it has gone to sleep. The car can happily sit for a few days now and still start.

 

[television]

Thats still double what it should be

 

[bigasotonuk]

Could an excessive drain be caused by a dodgy back-up battery in the alarm system?
If the back up battery was knackered it would be drawing excessive current to maintain its charge, just a thought, as the sirens are prone to failure.
Might be worth disconnecting the siren annd then rechecking the battery drain.