SLK battery change

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Eyeball Paul

New Member
Joined
Apr 5, 2013
Messages
2
Car
S320 & SLK200 (E240 & C180 in the past)
Hi, does anyone know if the ECU has to be adjusted if the battery is changed?
I was told it was best to have the battery fitted by a Merc garage as they would need to check the ECU would charge the battery at the correct rate etc.
Is this true or just "hogwash"!?
Thanks
Paul
 
Haven't got a clue probably is Hogwash , but it would be useful to know.

Michael.
 
Your SLK200 is pre-2014? It would have the same M271 engine as my W203, in which case this is not true....

Also - 'ECU would charge the battery at the correct rate' - the ECU does not charge anything, let alone the battery...

Sounds odd, probably hogwash...
 
Thanks - I do think he meant that the ECU would tell the alternator what rate to charge at but again I'm not technical so would not know if this was untrue. Car now in with dealership but think I may just get my own battery and fit myself - had no problems doing this on my E240
 
I've changed the battery on my SLK, (2005 MY 280), twice without any ill effects. Just follow in full the procedure in the handbook especially the part regarding which + and - cable to remove first and last thats all.

If anything, only the clock needs to be re-set and the window pinch points.
 
Thanks - I do think he meant that the ECU would tell the alternator what rate to charge at but again I'm not technical so would not know if this was untrue. Car now in with dealership but think I may just get my own battery and fit myself - had no problems doing this on my E240

Lead Acid battery charging on cars is quite old technology even on modern cars (bar EVs and Hybrids which typically use different battery technology) - so I would be surprised if the battery charging was electronically controlled by the ECU, as opposed to controlled locally by the Alternator.
 
My Blue efficiency petrol does have some control of battery charging voltage and modulates it to save fuel. I don't know the full details of when it's supposed to charge and when it doesn't but I've monitored it while driving and the charge voltage is all over the place. It's as high as 14.6 volts for a while after a cold start then at idle or when cruising if there is no substantial electrical load it will fall to the high 12's. It rises back up above 14 volts on the overrun presumably taking advantage of the free energy. Can't imagine it saves a lot of fuel but MB will have been trying to get the head line CO2 figure down.
 
Changed my battery on Saturday on my 2005 r171, had the original MB battery in there, did a straight swap and nothing needed adjusting, even the clock reset itself. Happy guy
 

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