Mercedes S350 W221 - 2012 - Digital Speedo Screen goes blank on Start up

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Rich2166

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I generally connect with the other car idling, if their battery is in good condition you can connect with their engine off

Many Thanks Blobcat, I will give that a go and see what results I get, I appreciate the advice
 

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if its the stock AGM battery from Merc, (they want 400 quid for it) under the label (where you'd expect to find them) are 6 screw top lids, undo and look. you will see bone dry white tissue paper and 6 black 3mm wide bits (the plates you shouldn't see). The tissue paper dries out in 3 years and the battery becomes 50% effective (but as such a monster if you use once a week you'll never know).

If you put about 120ml of distilled / de-ionised water in each cell - wait 30 mins and see if the tissue swelled up and covered the plates, if not add another 50ml to the dry ones, then charge for 24 hrs....

After 6 months of normal use it will be back to 95% of where it was and last another 3 years trouble free.

I believe on your car the baby battery in the boot is to control the start stop and make stuff behave when it cuts out in traffic... best left broken (stops start damages the engine)
 
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Rich2166

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This is my Battery, it does state Sealed Battery - Do Not Open? But I can see the plastic caps under the label
 

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Blobcat

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This is my Battery, it does state Sealed Battery - Do Not Open? But I can see the plastic caps under the label
Open it up as per Botus above, I’ve recovered Mercedes batteries the same way
 
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Open it up as per Botus above, I’ve recovered Mercedes batteries the same way

Yes, Thanks Blobcat, I’m going to indeed follow Botus advice on hopefully extending my Battery life
Appreciate everyone‘s help and input
 
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update: For anyone who’s interested I connected another car battery to my battery as mentioned
and started my car, the car started swiftly and the speedo display didn’t go off at all. Exercise complete ✅

Conclusion it’s my main battery that needs attention as kindly advised by Botus,
So next job is to get hold of a battery charger, top up the battery and fingers crossed this breathes
New life into my battery so I don’t have to replace this one to.
 

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you can see the shape of one of the screw top lids in your photo (on the right in the white bit of the label...)

they are a right nightmare to get out.... a bit of lube helps (not so much it goes inside), they are double a O ring design with the bottom one dry and stuck very hard and the flipping design is odd …. I eventually managed after substantially tweaking the bung at its top with a small flat screw driver so some lube just reached the bottom one and with a second pair of hands and two sets of long noised pliers...

Having only just nipped them up with some silicone lube on the O rings last time, when I opened it up a second time last year, I nearly gave up they were welded on with super glue and 20 armed thugs trying to stop them coming out.... INCREDIBLE

something like a valve cutting tool is required and then it would be easy - conventional right hand screw thread but the top of the bung falls to bits... hoping to nudge then round with a flat blade screwdriver and a hammer does NOTHING - all that happens is you make it harder when you try the pliers idea - which is the only thing that works

on a 10 year old battery, they seem to need about 150ft lbs to get then to move... once you unscrew and see it was 100% designed to come out you'll sit there and wonder how they put up such a fight
 
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Blobcat

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you can see the shape of one of the screw top lids in your photo (on the right in the white bit of the label...)

they are a right nightmare to get out.... a bit of lube helps (not so much it goes inside), they are double a O ring design with the bottom one dry and stuck very hard and the flipping design is odd …. I eventually managed after substantially tweaking the bung at its top with a small flat screw driver so some lube just reached the bottom one and with a second pair of hands and two sets of long noised pliers...

Having only just nipped them up with some silicone lube on the O rings last time, when I opened it up a second time last year, I nearly gave up they were welded on with super glue and 20 armed thugs trying to stop them coming out.... INCREDIBLE

something like a valve cutting tool is required and then it would be easy - conventional right hand screw thread but the top of the bung falls to bits... hoping to nudge then round with a flat blade screwdriver and a hammer does NOTHING - all that happens is you make it harder when you try the pliers idea - which is the only thing that works

on a 10 year old battery, they seem to need about 150ft lbs to get then to move... once you unscrew and see it was 100% designed to come out you'll sit there and wonder how they put up such a fight
I knocked mine round with a screwdriver and hammer, mashed the tops but they unscrewed and sealed back up again afterward. 2018 battery and dry as a bone
 

alexanderfoti

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I knocked mine round with a screwdriver and hammer, mashed the tops but they unscrewed and sealed back up again afterward. 2018 battery and dry as a bone
The car must be overcharging them for an AGM to be dry!
 

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The car must be overcharging them for an AGM to be dry!
It was below the plates, came back well and no issues with it (or the Sprinter it came off) since
 
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you can see the shape of one of the screw top lids in your photo (on the right in the white bit of the label...)

they are a right nightmare to get out.... a bit of lube helps (not so much it goes inside), they are double a O ring design with the bottom one dry and stuck very hard and the flipping design is odd …. I eventually managed after substantially tweaking the bung at its top with a small flat screw driver so some lube just reached the bottom one and with a second pair of hands and two sets of long noised pliers...

Having only just nipped them up with some silicone lube on the O rings last time, when I opened it up a second time last year, I nearly gave up they were welded on with super glue and 20 armed thugs trying to stop them coming out.... INCREDIBLE

something like a valve cutting tool is required and then it would be easy - conventional right hand screw thread but the top of the bung falls to bits... hoping to nudge then round with a flat blade screwdriver and a hammer does NOTHING - all that happens is you make it harder when you try the pliers idea - which is the only thing that works

on a 10 year old battery, they seem to need about 150ft lbs to get then to move... once you unscrew and see it was 100% designed to come out you'll sit there and wonder how they put up such a fight

Ohh, that sounds a fight I should of known it wouldn’t be easy.
Did you take the battery out to remove the caps, and if so did you have an issues when you put it back in, like having to put in radio codes, engine immobiliser /alarm issues, or did you just put back in and connect it up with No problems.
 

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it will be just as easy in place...

you need the car unlocked or the alarm goes off
windows and sunroof anti-trap need a reset if the battery comes off… but being there's no room on yours and it 23kg I'd leave well alone
 

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my AGM on the R1200 GS just stopped working one day... popped the tops off, each cell needed 140 ml (out of I guess a max of about 200ml), gave it a charge and its been happy as larry for the last 3 years, pop a charger on it these days and it cuts out in 30 seconds not needed
 
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Rich2166

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I checked my battery today with a multi meter and with the engine switched off it measured 12.08
leaving the probes in place started the engine the reading dropped to 8.87 then kept rising until
it reached and stayed between 14.08/14.10/14.11

I took the car for a run for about an hour and half and checked if the battery had any charge put into it
On my return but I was surprised the reading showed 12.02 - even lower than before the long drive.

Next step is to attempt to get the caps off, although I thought it would give me more access taking
the battery off, although I know I will have to synchronise the Windows, Steering, Sunroof.

Also a note that I don’t have a house with a drive, so leaving the car outside is an issue, and to charge the battery
the battery would have to come out the car, so I am torn what to do?
 

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12.08 is the issue, too low. Get the screwdriver out and start butchering those lids ;)
 

Botus

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to some extent just getting that tissue damp with have the effect u need....

a long steady charge is a nice extra.... it'll charge as u drive but with some conductivity between the plates it might remember what the alternator is trying to say ;)
 

kennymerc

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Many Thanks Kenny,

I’ve only just replaced the Auxiliary Battery on Friday, so having to replace the main Battery as well is something
I really could of done without. Did you end up having to replace your Auxiliary Battery at the same time?

With the Auxiliary Battery I was advised to only fit a Genuine Mercedes one due to it being Voltage critical
however I wonder if it’s the same with the main battery as well, or whether I could fit an alternative brand?
Hi, Sorry for late reply, I replaced under bonnet battery with Genuine Merc. As stated earlier it solved the issue 100%.

rgds Kenny
 

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