W211 - Battery drain?

[DY2]

Good afternoon...


Recently changed the Battery Control Module on my 2003 W211, due to corrosion in the electric connector.
Battery has also been draining...
Charged it up... started the car fine... put a multimeter on the main battery... showed 14.5v (alternator working as should?).
Next morning, car won't start....
Gave the main battery a good charge again and reconnected it.
Went to take the car out later in the afternoon... no go. Car won't start.
Recharged the battery overnight...
Next morning, Car started fine... took her for a drive. All ok.
Later that afternoon... car won't start...
Put a multimeter on the main battery... volts were 11.5 - within 5 minutes, it shows almost 11v.

Could the battery be knackered?
Could something drain it that quickly?

 

[mersum1es]

Unfortunately you need measure curent draw, and then start pulling fuses until you (hopefully) find a source. Remember car needs to 'go sleep' after fuse is put back (about 5 min waiting).

 

[Oldspanners]

Good afternoon...


Recently changed the Battery Control Module on my 2003 W211, due to corrosion in the electric connector.
Battery has also been draining...
Charged it up... started the car fine... put a multimeter on the main battery... showed 14.5v (alternator working as should?).
Next morning, car won't start....
Gave the main battery a good charge again and reconnected it.
Went to take the car out later in the afternoon... no go. Car won't start.
Recharged the battery overnight...
Next morning, Car started fine... took her for a drive. All ok.
Later that afternoon... car won't start...
Put a multimeter on the main battery... volts were 11.5 - within 5 minutes, it shows almost 11v.

Could the battery be knackered?
Could something drain it that quickly?

How old is your battery?
If it has been undercharged for some time it may well be finished. Check the electrolyte level in the cells and look for a low level in one or more cells. Would have to be a big drain to flatten a good battery in that time.

 

[DY2]

How old is your battery?
If it has been undercharged for some time it may well be finished. Check the electrolyte level in the cells and look for a low level in one or more cells. Would have to be a big drain to flatten a good battery in that time.

Battery is a good 4-5 years old now

 

[Oldspanners]

My "guess" would be the battery. if you can charge it and leave it disconnected over night and try it in the morning and it still doesn't start or struggles that should prove it.

 

[AMGeed]

Any chance of borrowing a known good battery and seeing if the same thing happens overnight.
If it doesn't, it does point to a duff battery.

 

[joderest]

charge the battery, it should show at least 12.5 volts, leave overnight not connected, if it has dropped a lot, then its the battery, if it has not dropped, reconnect to car with ma meter connected in parallel with negative lead and see what draw is.
I cannot remember what is acceptable 35 ma ? I could be incorrect.

 

[AMGeed]

I was told up to 65mA is an acceptable current draw.

 

[Tony Dyson]

charge the battery, it should show at least 12.5 volts, leave overnight not connected, if it has dropped a lot, then its the battery, if it has not dropped, reconnect to car with ma meter connected in parallel with negative lead and see what draw is.
I cannot remember what is acceptable 35 ma ? I could be incorrect.

Meter would need to be connected in series not parallel to read current and be careful as any draw greater than 10A will at best blow fuses or the meter itself if it's a budget model, 35ma should be acceptable.

 

[MJJ]

As said above, you really need to connect your multimeter between the battery +ve terminals, and the removed +ve cable, so the meter measures the amps flowing from the battery.

Then, wait for the car to go to sleep (15 mins) and start removing fuses one by one. When a removed fuse makes a substantial difference to the current draw, you then need to investigate what circuits on the car are protected by that fuse. This helps you narrow down what is faulty, and causing the draw.

This post of mine - https://forums.mercedesclub.org.uk/index.php?threads/battery-drain-211.182200/#post-1826399 - gives some detail from WIS of what a healthy current draw should be, <60mA when the car is asleep. On my S211, the alarm siren was the source of the current draw.

I seem to recall at the time when I was diagnosing mine, that the genuine Mercedes iPod adaptor kit and the installed telephone were also common causes of current drain.

Martin.

 

[Botus]

if its an AMG battery and your are think of discarding put 60ml of distilled water in each cell and see how it is in a week

I thought we used to get lots of posts on this era e class with the door handles filling with water and shorting something out.... the fix was new painfully expensive door handles

 

[joderest]

opps, said i might not be correct, i always used negative lead>> meter>> battery to see what is being drawn (never was a good auto electrician !!!)