Replacing one's own battery

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Phil1968

Active Member
Joined
Mar 22, 2015
Messages
585
Car
C219 CLS 500, W447 Vito 119 CDI
I'll be replacing the main battery on the CLS this weekend. Do I have to provide a constant 12 volt DC source to the battery leads during the swap over so any system memories aren't lost? I have a spare 12 volt motorcycle battery I could use.
 
I have swapped batteries before by jumping another across with leads - to a chassis earth + to live under the red jump flap.
quicker than resetting clock,date, windows, sunroof.and audio.
 
Just remember that after you have connected the slave battery the main leads are still live so when you disconnect the main battery make sure the battery leads do not touch anything important, whether on the car or you! (I was years ago bitten by a fully charged heavy duty Land Rover battery and still have the scars!).
 
How did that happen?....its only 12v... that is no where near enough Potential difference to electrocute anything. You can put a hand on each terminal and you won't feel anything......unless of course you were messing with a live ignition coil..... they sting a bit due to several thousand volts that make! I guess if you touched a live terminal at the point it was shorting to the earthed body it might hurt a bit due to the heat generated.
 
There is a HOW TO video thread in the forums HOWTO section I created a couple of years ago - I actually filmed with my CLS:

 
Nice video. +++ for having tha camera in a fixed position while showing the process.

There are however a few hints that I would like to add that will keep many settings
unchanged so that they will not have to be re-entered after a battery replacement.
The procedure below is used at least in the MB authorized workshop where I go for
advice and have my car for annual service.

Don't take this as a critism. Just some friendly comment.

1. Open the driver side window and keep it down.
2. Open the hood or luggage compartment where the battery is located.
3. Close all doors. Lock the car and move any key-less key well away from it.
4. Wait some 30 minutes for the car to go into sleep-mode.
5. Replace the battery as shown in the video.

The reason for taking down the driver side window is that IF (!) the car looses
the key code setting, the door can always be opened manually from the inside
and the key transponder will be able to connect to the ignition system.
The procedure is adviced, possibly because of "accidents" that had happen
in Mercedes cars in the past. Most likely not applicable to todays models
but IMHO an advice that should be in mind.

Also, having the car gone into sleep mode should make all window
settings kept without the need for recalibration.

When I replaced the battery in my C207, I also removed/lifted the bottom plate
up for inspection, found a lot of "vegetation" that had gathered over the years
blocking the drainage. After removing all dirt, I noticed that one of the bolts
used for the bottom plate was right above one of the AC aluminium tubes.
That bolt has to be the short one when reassembling the bottom plate after
cleaning out all the dirt.
 
How did that happen?....
Checking the Rover after a day's work scouting a route for a planned rig move in Baluchistan (Pakistan), got a spanner across the +ve, my metal watch strap and part of the car, big spark and swearing as watch strap had welded closed and felt like it was burning through my wrist. Took one of the lads with a screwdriver to open the strap and take the watch off - to him it felt cold! 2 small round scars inside of left wrist still slightly visible to this day - and it happened in 1975!
 
Ouch.......
 
Just remember that after you have connected the slave battery the main leads are still live so when you disconnect the main battery make sure the battery leads do not touch anything important, whether on the car or you! (I was years ago bitten by a fully charged heavy duty Land Rover battery and still have the scars!).
My father managed to do something very similar in the early 70s swapping out a Ford Transit battery. The spanner he was using to undo the positive terminal touched the bodywork & a ring on his finger was in contact with the spanner, he ended up with a permanent scar in the shape of the ring on his finger!
 
My grandfather was in the REME and as a kid I remember watching him working on his cars at home. The first thing he always did was remove his watch and wedding ring.
 
I used to work for an ex REME man - he said the initials stood for "Rough Engineering Made Easy!"
 
When I changed the battery on my 2012 C- class I didn’t attach anything else. I did the swap in less than a minute and didn’t lose anything, not even the radio code. There’s plenty capacitance in the systems for short-term storage.
 
My father managed to do something very similar in the early 70s swapping out a Ford Transit battery. The spanner he was using to undo the positive terminal touched the bodywork & a ring on his finger was in contact with the spanner, he ended up with a permanent scar in the shape of the ring on his finger!
Which is of course why we disconnect the negative first and reconnect it last!
 

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