Very high battery drain

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badmoon

Active Member
Joined
Dec 17, 2013
Messages
62
Location
Milton Keynes
Car
W221 S500L
Hi My W221 S500 has just developed a parasitic draw of 10 - 11 amps resulting in a flat battery within about 3 hrs from fully charged Plus it will only charge if it’s disconnected
I have just the handbrake actuator changed and also the air suspension pump changed within the last 72 hours
Any suggestions please
 
Can you disconnect these circuits or pull the fuses to see if the drain continues, 11 amps is quite high and could cause overheating. I would be inclined to disconnect the battery overnight/when unattended.
 
11 amp at 12 volts is 132 watts if my sums are right so something is getting pretty warm. (Warmer than two headlamp bulbs on main beam) So finding it shouldn’t be too much of a problem.
Does your car have a block heater? I’d be checking that (or the control relay for the block heater.)
Another less likely cause could be the seat controller/motor stuck but tbh I don’t think it would take 11 amps and you would likely smell it at that rate.
 
Hi My W221 S500 has just developed a parasitic draw of 10 - 11 amps resulting in a flat battery within about 3 hrs from fully charged Plus it will only charge if it’s disconnected
I have just the handbrake actuator changed and also the air suspension pump changed within the last 72 hours
Any suggestions please

Those numbers don't stack up? Assuming your battery is 75 Ah or so you'd need a much higher current (25A) to flatten it from fully charged in 3 hours. 11A for 3 hours is only 33 Ah.

But as suggested start pulling fuses one by one till the drain stops ... then you know which circuit is the problem and can investigate further. 11A is nearly 140W so something should be getting pretty warm. 25A is over 300W ...
 
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Those numbers don't stack up? Assuming your battery is 75 Ah or so you'd need a much higher current (25A) to flatten it from fully charged in 3 hours. 11A for 3 hours is only 33 Ah.
I was going to mention that but battery capacity is measured at the 20 hour rate, so a fully charged 75Ah battery in good condition will supply 3.75 amps for 20 hours.
Increasing the load will considerably reduce the stated capacity.
Still seems a bit low on capacity though 👍🏻👍🏻👍🏻
 
It could be the alternator. A failed diode or faulty regulator can drain the battery quite quickly.

 
Thank you all for your suggestions I have tried pulling the fuses for the recently changed items but the drain remains the same I will start tomorrow pulling all the others The battery is currently disconnected and on trickle charge over night When it was connected and using a powerful charger it could not get above 5.5 v as the drain was too severe Also I cannot find anything getting hot nor smell burning
 
Well if you have a meter on the battery and its showing a draw when everything is switched off I would start to pull fuses and see if the draw stops or get a mobile car electrician to sort it,chances are that it is something to do with the recent work you have had done on the car
 

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