battery looses charge if car not used

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mcoy

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May 4, 2006
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if i do not use my C270 (2001) for 2 days the battery goes flat, how can i check out what is draining the power?

thanks for any suggestions
 
Almost certainly it just needs a new battery (assuming it still has the original one from 2001 in it).
 
BTB 500 said:
Almost certainly it just needs a new battery (assuming it still has the original one from 2001 in it).

I agree, they should last for weeks not days.:crazy:

Get a new one and save the aggro mate.
 
already changed the battery, something must be draining it slowly, any ideas how i can test what is drawing current with the ignition off?
 
Do you have Command at all?

Alternatively, it could perhaps be the alternator that is at fault and not charging the battery after usage but a faulty alternator should give an error code on the MFD I would have imagined.
 
This may take a while to diagnose. If you are not confident weilding a screwdriver then its best left to an electrical specialist.

Check all the obvious like the glove box light and boot light are switching off when you shut them.

The next step is to buy a multimeter (a reasonably good digital one) and then measure the current drain in series from the positive lead to the battery.

One by one remove each fuse in turn and see which circuit is responsible for the drain. Once you have the circuit narrowed down, you need to inspect it thoroughly looking for the cause of the problem.

Common causes are alarm systems, or faulty windings on a starter motor/alternator.
 
You'd be looking for a constant drain of about 1.5 amps (18 watts) if the battery is really going flat in 2 days ...
 
mcoy said:
already changed the battery, something must be draining it slowly, any ideas how i can test what is drawing current with the ignition off?

Something may well be keeping awake the SAM (fuse box) modules and that takes about 600mA constant waiting for network traffic.

A professional will examine current draw on the front and rear fuse box and then selectively disconnect CAN lines or fuses until the "sleeper" current drain is switched off.

The reason you may need an expert is to distinguish between normal CAN activity (which increases when you open a door and so on) and dormant but irregular CAN activity.

Memory seat modules are common culprits.
 
BTB 500 said:
You'd be looking for a constant drain of about 1.5 amps (18 watts) if the battery is really going flat in 2 days ...

Looks as though it may be a bulb lit somewhere.
 
Most commonly the seat control modules. Unplug these under the seat and see if it fixes it. 9 out of 10 times it's these.
 
Thanks for all your replies, i'll try some of your suggestions and let you know. The car has a command system, sat nav and electric everything!

thanks
 
Geoff2 said:
Looks as though it may be a bulb lit somewhere.

Yup, drain seems a bit high to be electronics.

That's assuming the battery is being charged properly in the first place, of course ;)
 
mcoy said:
if i do not use my C270 (2001) for 2 days the battery goes flat, how can i check out what is draining the power?

thanks for any suggestions

Any news yet?

John
 
If there is no obvious cause, before you drive yourself nuts trying to find the problem take the car to a reputable (cough, splutter) outlet for batteries and ask them to test.

Sadly modern batteries suffer because the constant drain from electonics. Once a battery has deeply discharged it is for ordinary purposes done for. Can treat them but less hassle to get a new one. And the biggest that will fit.

Bear in mind that the "average" life of a battery in the UK is reckoned to be somewhere between 3 to 5 years
 
Completely agree, but this is a new battery (post #4).
 
My gut feeling has always been a battery but I also noted post #4 hence my request for an update.

John
 
I know that this is an old posting, the way to do it is to join a ammeter in serries with the battery, try and do it without breaking the circuit, as some faults could correct themselves, and take the fuses out 1 by 1, it is much easier to have someone watch the meter. I would start with Command fuse.

Malcolm
 
The best way to do it is with a DC clamp ammeter round a main cable from the battery, if you know someone who might have one.
 
BTB 500 said:
The best way to do it is with a DC clamp ammeter round a main cable from the battery, if you know someone who might have one.

The snag here is that a DC current clamp meter ,capable of measuring DC m/a with a resolution of 10m/a cost a minimum of £135 where as a multimeter costing just £5 would do the job. There are plenty of cheap AC current only on the market, but of no use for this job or on a car.

A clamp meter has very limited or of much use on a car with 2 batteries or more.

We do not loan out test gear, and no one else in their right mind should either.

Malcolm
 
television said:
The snag here is that a DC current clamp meter ,capable of measuring DC m/a with a resolution of 10m/a cost a minimum of £135

However you can buy a 0.1A resolution clamp meter for £55, which would be fine for this job since we're looking for a drain of around 1.5A.
 

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