Battery drains, car won't start - Page 2 - Mercedes-Benz Forum

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post #11 of 12 (permalink) Old 10-16-2010, 02:48 PM Thread Starter
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Date registered: Sep 2010
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Not the battery, no COMAND

The initial post did say that it wasn't the battery, but I should have stated explicitly that I'd replaced it.

I do not have COMAND with Nav.

My mechanic says that some of the circuitry in the car (mainly computers, I gather) is unfused and capable of draining the battery overnight.

Originally Posted by keyhole View Post
OK - we belatedly learnt that you have a brand-new battery.....

Let's ask another question. Do you have COMAND with Nav?
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post #12 of 12 (permalink) Old 10-16-2010, 04:38 PM
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Originally Posted by aorrdalca View Post
When the car sleeps, the draw is ~ 20-30 mA. I'm not sure whether my mechanic, who is very good and has lots of experience with MB, has an SD scan, but is this something that can be done in '04 models? I seem to remember that MB recently beefed up the on-board power diagnostics, probably in response to complaints like this.

I have seen a number of other posts like mine, and many seem to have as a precipitating event the inadvertent flattening of the battery.
20-30ma is well within spec. on your car when everything is asleep you should see between 10-80ma, if you see over 100ma then something small is staying on. usually main computers that arent going to sleep draw over 500ma to several amps. now everything in the car is fused. there are no control units that arent fused. all units have a power supply and that power supply is fused which comes from a main fuse box. now if the car dies after a day or so with a new battery then the draw shouldnt be hard to catch. sometimes you have to keep watching the meter as the readings will jump. this is where the sd scan comes in it does the monitoring for you so you can do other things. more then likely an indy mechanic wont have the software, in that case he will need to watch the meter for a jump in the readings. but again 20-30 ma is a good reading.
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