Charging a very flat w211 estate battery

orcwrath

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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?
 

geoffus

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Sounds like a good idea, unless you have an older type battery charger to connect up ?
If you connect up the jump start battery from your other car, then boot should open up within a few minutes, you shouldn't need to try to put charge into the duff one.
 

markjay

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What’s the stamped date on the battery terminal ?

And does it say 'Mercedes-Benz' and 'Varta'.....................................?
 

pmcgsmurf

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No way I would be connecting another car to a dead battery.
20 amps plus = burnt out jump leads at best at worse all sorts of electric problems.

If you really cannot get to the battery then connect a high amp charger but you will likely need very high current one.
 

m80

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An 08 shouldn't be as delicate, but the spike would take out SAM's on earlier mo mo's as you connect up to the higher voltage donor.Consider engine off, lights on as you connect.

I would forget the running car, faster charge set up, in favour of a slower transfer.
The volt drop across the leads should be a good protection for the 211 anyway.

As your duff battery picks up some, say 11 volts, if the smart charger has pulse consider removing the battery to go on a repair charge. You might be lucky, but it depends on how reliable you need the car to be.
 

geoffus

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If the donor battery is normal 12v and it is connected parallel to the duff battery via the jump terminals, then there wont be a problem.
The so called "spike" while jumping is mythical if done correctly.
 

pmcgsmurf

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I think jump leads will do more than 100 amps.
Why would it cause problems?

Most people don't have high quality jump leads.
I've a 3000 Amp set here that the guys always joke to me could start a jumbo jet.

A cheap set and a high current draw is not a good combination.

As i said I'd get the battery out and charge it and if I really could not I'd stick a big charger on it.

I've seen so many folks with problems on moderns because they tried to jump start another car, connected up wrong, dropped a lead and caused a short or any combination of other things.
 

Petrol Pete

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Me too ^^^ get into the car far enough to remove the battery and try charge it up on the bench, no joy ? Buy a new battery.

On a 2008 car it might still be the original battery so replacing it might be a good move.
 

geoffus

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But if he has decent jump leads and all he wants to do is apply enough power to open the boot via central locking, then no problem.
The cars battery could be high resistance so may not draw high current anyway, all he wants is to do is get at the battery and then prob chuck it away.
 

MikeInWimbledon

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How smart is your smart battery charger? GCSE or Graduate ?

If it's not a CTEK, it would be worth trying a CTEK on it, if you can beg, steal or borrow one from a mate.

I'm not "being cheap," I'm being Greta.
 

wongl

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Do this sound reasonable or doomed to failure?
This is risky - several owners have experienced problems after 'jump starting' their cars. I know you are not technically 'jump starting' your car, but there are risks nevertheless. You will see a number of posts of owners connecting the jump lead the wrong way round and taking out several fuses at best! This is an easy mistake because the original MB battery is black and the terminals are not color-coded.

I would personally avoid doing this at all costs, and would not recommend this approach to my friends/family. I have actually purchased a cheap low ampere trickle charger solely for recharging dead batteries to bring them up to a respectable level before putting on my CTEK charger.

The latest Aldi 5A smart charger at £16.99 looks interesting as they claim it can charge a dead battery! For a 5A charger, it is a cracker at £16.99, but the ability to charge a dead battery is an absolute plus. I have ordered one online, and if it can really charge a dead battery, I can throw our my trickle charger!
 

wongl

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How smart is your smart battery charger? GCSE or Graduate ?

If it's not a CTEK, it would be worth trying a CTEK on it, if you can beg, steal or borrow one from a mate.

I'm not "being cheap," I'm being Greta.
I have two different models of CTEK chargers, and good as they are, I don't believe either one can charge a dead battery.
 

geoffus

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This is risky - several owners have experienced problems after 'jump starting' their cars. I know you are not technically 'jump starting' your car, but there are risks nevertheless. You will see a number of posts of owners connecting the jump lead the wrong way round and taking out several fuses at best! This is an easy mistake because the original MB battery is black and the terminals are not color-coded.
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.
 

MikeInWimbledon

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I have two different models of CTEK chargers, and good as they are, I don't believe either one can charge a dead battery.

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.

You specifically select "Supply mode," not normal charging or reconditioning.

Maybe worth a try ?

Here's the manual:

https://www.ctek.com/storage/7514D4...85f3914e80f67532/MXS_7.0-manual-low-UK-EN.pdf
 

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