Charging a very flat w211 estate battery

alabbasi

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Feb 18, 2008
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So my 08 W211 estate has a very flat battery, no central locking and the ignition key wont even engage. My "smart" battery charger won't even start charging, so I'm assuming that the battery is currently below 2V. My plan is to:

  1. use jumper leads from my other car to connect it's battery to the jump start points under the W211's bonnet
  2. start the other car but not the W211 and not turning the w211 ignition on
  3. leave the other car running for about 15 minutes, this will hopefully also give me access to the w211 boot so I can find the type of battery fitted
  4. turn off the other car, disconnect the jump leads
  5. try the "smart" charger again on the jump points to do a full recondition/charge, as the battery should now be over the 2 V limit
Do this sound reasonable or doomed to failure?

Plug a jump box on the battery but don't start it. Let the jumper charge the battery for 20 minutes than use a smart charger to do the rest.
 

wongl

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The problem is he cannot get at the battery, its in the boot, so is connecting to the jump start posts under the bonnet.
Surely that's the easiest job to do, and very difficult to do wrong, its not scary.
The battery is duff but needs to get at it to remove and replace.
Not a problem as you can still trickle charge the battery in the boot via the jump-start points in the engine bay.

You will be surprised how many people do get this wrong!
 

wongl

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If you google, you'll see that a CTEK 7.0, or later, with "Supply mode" can be used to revive a dead battery which doesn't even have 2.0 volts.
Ah, I don't have anything as powerful as that. I only have an MX3.8 and a CT5 Start-Stop charger. Neither will charge a near-dead battery, let alone a dead one!
 

markjay

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Remove both batteries from the vehicles.

Connect the two batteries in parallel.

Connect the trickle charger, it will start charging both batteries.

After a while you can disconnect the good battery, the trickle charger will continue to charge the flat battery.

(No electronic components on either car were damaged in the production of this charging rig)
 

MikeInWimbledon

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Nov 8, 2014
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Previously C216, CL500 S212 E500, W211 E500 5.5, E350, W221, S211 E500, SL350, SL500, S500, E55
Rent one for £25 ?

Yours from Halfords for £100 (if a friend or neighbour doesn't have one.)

CTEK Multi MXS 7.0 Battery Charger | Halfords UK

Connect it to the connection points in the engine bay and away you go.

Sell it for Ebay for £75 if you don't want it afterwards.



280326
 

Flyinspanner

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And once you get the battery off... it may be worth opening the cells and checking that the electrolyte actually covers the plates.
top up with demineralised water.

It might help.
 

Blobsta

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Mar 13, 2013
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Maidstone, Kent
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Take the battery(ies) out and connect a cheap eBay charger that does pulse charging, I bought one last year for about £20 but with the amount of flat batteries around, chargers have shot up in price so the same thing is almost £30 now. I wouldn't pulse charge it on the car as we know how MB electrics love a reason to get their knickers in a knot but off the car it will be kill or cure. Either way as others have suggested you probably need a new one.

Don't suppose you are anywhere near Maidstone are you? I have a trade account at MB locally and their battery prices on that are very reasonable. I'd be happy for you to use my discount, it helps to bolster my account and its money over their counter as far as they are concerned. To be fair that goes for anyone local to me, I'm not trying to make any money from it; but it helps us all.
 

OneForTheRoad

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uk.
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OP
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orcwrath

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Mar 5, 2006
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5
Thanks for all the responses, with the warmer weather the voltage was high enough for my Ctek MXS 5.0 to start a charge and recondition. Got the car started and I'll keep an eye on it for now but looks like a new battery sometime in the near future.
 

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