W221 Battery removal problem

tode

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Good evening all,

I'm having a little problem with my S350 bluetec -- I want to change the main battery in the engine compartment. I've undone the top battery clamp but there must be another clamp on the foot of the battery (on the right in the photo):

BATTERY SITN 800 AN.jpg
The problem is that there's a black box (starter relay ?) at that end of the battery which covers the clamp and its bolt and for the life of me I can't get the little rascal out.

BATTERY DETAIL  800 AN.jpg

Does anyone know how to remove it ? Or have the WIS instructions ? No visible screws or nuts - I think it's just clipped onto a bracket (?).

Your help will be much appreciated . . .
VIN = WDD2210261A441050.
 
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Xtractorfan

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The bottom clap is normally only a fixed bracket that the battery slides into, so once the top battery clamp has been removed try sliding the battery away from the bottom bracket and see if it will come free.
The black box on the side is usually only clipped into position.
 
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tode

tode

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Thanks -- I've removed the top clamp, but the battery won't budge at all :(

Do you know how the relay unclips ?
 

ajlsl600

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has it just become stuck? as stated normally the batt drops in and slides a bit to one side catching a preformed pressing in the tray acting like a clamp. if not plse post picture when you get it out showing clamp
 

DREAMER NO2

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As you have removed the top camp , you now have to move the battery in the tray one way or the other because the battery slides in to a preformed section on the side of the battery tray ,this is to hold it before its clamped down in place with the top clamp ..
 
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tode

tode

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Well, finally managed to get the relay out and the battery changed.

The problem was due to the relay support which also serves as the clamp for the battery base:

BATTERY CLAMP BASE.jpg

When this is fully screwed down the two vertical supports are forced against the battery wall. This in turn means that the two clips that hold the relay in place can not be sufficiently moved to release the relay.

My solution was to force the relay away from the battery with a large screwdriver, insert 3mm wedges to hold the relay away from the battery and then release the two clips. Ideally, you need three or four hands, but I made do with two . . ;)

Before installing the new battery, I bent the relay support to ensure a 3 - 4 mm gap between it and the battery when fully screwed down (for next time :rolleyes: ).

This is the relay seen from the back. The support is inserted into the two slots (red arrows).

BATTERY RELAY 01.jpg

No resets were necessary afterwards.

Thanks to everyone for your suggestions :)
 

DREAMER NO2

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Well you learn more every day .Not fixed in as we thought like most battery. Well it was like most others only mercedes utilised the clamp to hold the relay .
 

ajlsl600

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well pictured ..and a new example of car maker making a simple job considerably more complex than it could ever need to be.. wots new!!!!!
 

Johndaly55

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Well, finally managed to get the relay out and the battery changed.

The problem was due to the relay support which also serves as the clamp for the battery base:

View attachment 47088

When this is fully screwed down the two vertical supports are forced against the battery wall. This in turn means that the two clips that hold the relay in place can not be sufficiently moved to release the relay.

My solution was to force the relay away from the battery with a large screwdriver, insert 3mm wedges to hold the relay away from the battery and then release the two clips. Ideally, you need three or four hands, but I made do with two . . ;)

Before installing the new battery, I bent the relay support to ensure a 3 - 4 mm gap between it and the battery when fully screwed down (for next time :rolleyes: ).

This is the relay seen from the back. The support is inserted into the two slots (red arrows).

View attachment 47089

No resets were necessary afterwards.

Thanks to everyone for your suggestions :)
I had the same issue. Had tried google and you tube and was stuck until finding this thread. Thank you for solving it for me too.
 

Rich2166

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Excellent post Did you remove the battery whilst keeping a 12v connection, or did you just remove it and then run through the synchronising sequence?
 
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tode

tode

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No need to maintain 12V while changing the battery and no need for synchronisation aftrewards.
 

Rich2166

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No need to maintain 12V while changing the battery and no need for synchronisation aftrewards.

Many Thanks for the reply, can you explain how come you mention you don’t have to maintain a 12v connection whilst changing the battery as a Mercedes tech told me I do. My car is a 2012 S350 Bluetec.

Many Thanks
 
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tode

tode

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I think it's a hang-over from previous models . . . ;)

The (main) battery has been out twice on mine and nothing needed resetting both times. The last time it was out for a couple of hours (while dealing with the above problem), but it's possible/probable that if the battery was disconnected for days a reset may be required - windows etc.
 

Rich2166

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Thanks Tode, That’s interesting, although with my luck if I don’t use the 12v live option,
I bet all my settings will disappear. I will have to see what I decide.
 

Rich2166

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I think it's a hang-over from previous models . . . ;)

The (main) battery has been out twice on mine and nothing needed resetting both times. The last time it was out for a couple of hours (while dealing with the above problem), but it's possible/probable that if the battery was disconnected for days a reset may be required - windows etc.

Tode you are a fine gentleman, thanks to your excellent post and images I disconnected the plastic relay box with the assistance of my partner in just 5 minutes by the time I moved the battery cables out the way etc, and removed the bottom battery clamp, it was a real simple job to do, already to fit the battery in tomorrow as the weather was not great today.

Anyone who is not sure how to change their battery can follow this post and easily do it with no problems,
just for anyone who’s interested, Mercedes Main dealer wanted £90 to fit a battery purchased from them, so it’s definitely worth doing the job yourself.

Also an important note:

Just to be on the safe side I’m going to use an Auxiliary battery connected to the battery poles to keep an active charge in the system, so I can guarantee I don’t lose any of my settings

Again much appreciation to you Tode for a very helpful and excellent post
 
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tode

tode

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Glad to be of help . . . :)

If it was the original battery, then 8 - 9 years old isn't bad.
 

Rich2166

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Glad to be of help . . . :)

If it was the original battery, then 8 - 9 years old isn't bad.

Yes Tode it was the original battery so 9 Years is exceptional, so I can’t grumble ;)
Keep in touch maybe I can help you with something at some point :)
 

Botus

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on the w221 there is no need to keep it alive…. *except for one recent bit of fun...

the car is perfectly happy take the battery off and leave it off. On reconnection then you always need to reset the anti trap for all 4 windows and the sun roof... which involves opening fully and closing whist holding the button all the way, for a few seconds when closed until you hear / feel a clunk.... That's normal for just about any car since 1995. Don't bother and they will still operate, but the one touch fully open or fully closed feature remains inactive.

*however the W221s time and date is set automatically by finding sensible info from the satellite flying in the stars above.... and with satellites resetting their reference for which part of a 19 years cycle they are in, on 6th April 2019, the W221 no longer makes sense of the info it receives.

keeping 12v on the vehicle as you swap out the battery is not really helping, as the car's now muddled and can get in a pickle over the daylight saving events anyway. This is where the digital clock and the analogue clock argue (usually seen as the analogue one won't behave). After ignoring and then informing dealers they would never bother to sort out. An American guy decoded a comand telematics update disc and reverse engineered a fix. As he's connected and got it right.... Merc eventually adopted his work and allegedly a dealer can fix it... if not a DIY is easy to do... except for the odd random car that doesn't seem to get over its headache, where the home made disc doesn't update the cars comand software like it should.

 
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