New battery. Keeps going flat.

Keith Johnson

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c220 kompressor
Hi everyone new to this forum.

My wife has just bought an 08 c220 kompressor. The car has been running great. But the other day she got up to go to work and the key wouldn't turn in the ignition. No lights no nothing. I tried to jump start it with no success. I thought it was the battery that might be on its way out so bought a new one. fitted it and the car started straight up jobs a godin. Took the car for a good run out parked it up as normally. About an hour or so later I needed to pop out but battery was dead again. The alternator seems to be charging the battery up as normal when driving and is being drained when parked up. If anyone has any idea I would be very grateful. Been trying to get it booked in for a diagnostic but everywhere seem busy at the moment.

Thanks again for any help
 

peterws1957

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sl350 /2004/3.7 and CL65/2009/6.0
What were the voltages of the old battery and the new one after you had taken the car for a run. Have you actually checked the output of the alternator? Even if you had a voltage drain its strange that the battery would discharge in an hour. If your wife bought from a trader I would be taking it back to get fixed. If a private sale the next step would be to get it on Star.
 

LostKiwi

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'93 500SL-32, '01 W210 Estate E240, 02 R230 SL500 (Malcolm Spec), 04 Smart Roadster Coupe
If these have a block heater they are known to cause a high drain on the battery and flatten them in an hour.
 
OP
Keith Johnson

Keith Johnson

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Thanks for the reply it's going in Monday to get sorted hopfully.
 

Submariner1

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CL500 2009 5.5
Thanks for the reply it's going in Monday to get sorted hopfully.

Dont rule out a faulty battery.
I changed mine (that was working), and then I had loads of problems inclu the battery voltage dropping to 9V. . Final result was, the brand new Mercedes Battery was faulty! ( note the first check didnt see it .... then the Diagnostics said “faulty replace battery - replace battery).
Mobilo swapped it for another new one and no problems.

It might be prudent you check the current drain with a clamp meter.
You need to sort that really before blaming the battery.

Plus look at LK suggestion first.

On mine it was essential to wait for the car to shut down ... this could take 15 - 20 mins.
A shortcut is to shut the doors and lock it with the bonnet open. But remember to push the bonnet catches shut. ( otherwise the car SAMs seem to wait for you to shut the bonnet ) That saves about 4 mins , and in total saves 12 minutes.
On my car they said the normal drain could be up to 50mA. Mine varies from 40 to 0 mA .
 

Flyinspanner

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Ruislip
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CLK320-A209 (sold CL500 & W168)
I too had a faulty battery after only 7mths.... it was an intermittent internal fail, which drove me a bit doo-lally at the time.....

Get the new battery fully checked out as step 1.
 
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Keith Johnson

Keith Johnson

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Thanks for the reply. I've had the battery and alternater checked and everything is running fine. I will give an update on Monday when sorted. HOPFULLY
 

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