W215 cl500 battery drain

[Sudesh]

So it's back to the usual CL500 battery drain. I bought a new battery for the car, installed it and it started ok, however after about 1hr or so, it's dead, won't start without a jump. Also the Windows are stuck they don't drop in the normal fashion where they should come down a bit when you open the car, then close when the door is shut. Central locking is playing up too. Anyone any ideas? I double checked the battery and its 100%. Something is really draining it bad, when plugged in.

 

[Ted]

If what you are saying is correct, and you have a fully charged new (good) battery (say 90-100Ah) and it is draining in an hour, then you are drawing around 1 kilowatt.
For that to be happening something must be getting extremely hot - so hot you couldn't miss it.

Something doesn't add up.

 

[Sudesh]

Hi Ted, I'll just nip out to the car now and check the AH of the battery. But YES the battery is brand new, only purchased it a few days ago from my local motor store that I always go too.

 

[Sudesh]

It says on the casing, 95AH 850A

 

[Ted]

Thank you Sudesh.
Then the possibilities are
1 The battery is not fully charged.
2 The battery is faulty (i.e. does not have the capacity stated.)
3 That there really IS a huge current draw (highly unlikely as you would smell and be aware of something hot)

The above assumes that the car started fine with jump leads which indicates that the starting circuit is ok.

My next step would be to fully charge the battery. That will eliminate no 1
If this works then problem sorted. If it doesn't, I would get the battery tested (it will beed to be fully charged for this)
If it tests ok then you do have a large discharge. A good auto electrician would be able to diagnose this, but tbh I think it is unlikely.

My gut feeling is the battery wasn't fully charged, and there may also be a significant drain (check with an ammeter in series with the battery) - seat motor controllers rings a bell.

Hth - and good luck getting it sorted.

 

[Sudesh]

I'll start doing that right now ted. I even left the car sitting unlocked after the battery died. So I'll go out now, put the volt meter on it to see what the reading says, then put the charger on it for a good full day. Then work from there. I gues I need to have the Windows reset too after that.

 

[markmifsud]

try to unplug the alternator, diode packs can go bad and allow a large reverse current to flow.