W221 Battery removal problem

[mogul]

Merci tode - your post and photos were of great help to me today when swapping out the battery on my 2013 W221 350 Bluetec.

Once the relay is unclipped from the clamp/bracket, there’s just enough give in the cables to move it out of the way to reveal the 13mm bolt down below.

I guess you might be able to get away with just loosening this bolt, but I ended up needing to completely undo and thankfully didn’t lose it when I pulled the old battery out (there are a few nooks and crannies where you could lose it bellow the battery tray).

It was a good time to remove a few wet leaves etc. from below the battery tray and it’s all back together now.

 

[tode]

Nice picture - showing the support and the relay together.

 

[mioba]

Good post and thanks for the follow up with the solution, I find MB batteries excellent value as they do last a very long time. I am on the second on my W220 (first lasted 13 years) and still on the original on my W251 (should change it this year)

 

[Botus]

Ummm not sure that's true anymore..

my fathers 2 1/2 years old one is not holding a charge any more - my replacement didn't last the 9 years the original did and was swapped out at 4 years and its replacement isn't holding a charge after 18 months...

just went to take the tops of his battery today (came up with an idea to dremal a few sensible slots to get good purchase) - I have to say my notes previously about how hard these are to remove is somewhat under calling it - three turns after bottoming out (are they mad ??? and two GLUED in !!!) two refused to unscrew and even after 5 turns each 100% flush so I got the screw driver out and taught them a lesson all 6 cells dry as a bone... its had about 600ml

 

[Tony Dyson]

I wonder what's going through the minds of these design wizards when they design a Sealed for Life battery, then build an open vent into it so all the expanded gasses can escape? They could at the very least build a condensate trap before venting couldn't they? My original 2014 batteries are still performing well in a backup power application tested in a couple of power failures recently with the bad weather!

 

[Botus]

Mercedes like to expand on that open vent idea with a tube out the boot floor picking up a vacuum the faster you go to ensure it dries out

 

[Botus]

A few weeks back I battled my father's 211 genuine Merc battery - trying to get the tops of the battery and get some much needed moisture on the tissue of the AGM battery - it seems happier.

But mine was a 5 year guaranteed YUASA one that started to slide down hill at 4.5 years and was swapped out for a brand new unit FOC. Trouble was it always seemed about as rubbish as the one that came out. Playing with diagnostic kit yesterday I was trying to get some grunt into it and it wasn't playing ball.

With the key on I was down at 11.5v on high rate of charge that seemed to do nothing. Then It decided its was a 6v battery with 7.5 volts then decided it was a camper van deep cycle battery and held it around 11.7v 2 hours of that and it had enough go to know it was an AGM battery and would accept that charging algorithm...

Ever since that went in it never liked to go about 12.7v even after 48hrs on charge - so I whipped it out the back and got that sticky label off (came off unlike merc ones), and the screw top lids are a better design - and not part glued in - and interestingly with 3 red seals of the screw top lids. Its just taken 400ml

Put it back in the car and magically it was at 12.6V and after 15mins on charge it had popped up to 13v which it never did in the last 3 years !!!

So the gist is they ALL appear to be making designed to fail AGM batteries, with only enough moisture to last 18 months, survive around 2 years and be very dubious at 3 years