The 2010-2013 S550 I'm told has a battery inside the front dash? What does it do? How do you know when it needs replaced?

 

Yes, there is a large battery under the hood for starting/consumables and a small motorcycle sized battery behind the dash to power the electronic transmission shift selector. You can research on this forum to get directions to access the smallish battery through the side of your dash with the door open. It only powers the shifter.

Earlier models of W221 from 2007 through 2009 used a large consumer battery in the trunk and a small starter battery under the hood.

 

Thank you for the reply. Would a low interior dash battery cause the main battery under the hood to die faster?

If you have the time, could you link to the post about that internal battery? Driving.

 

no - but they have fun electrics that like dealers to given them an expensive stroke

check the other thread - how to charge the car and how to change that battery

https://mbworld.org/forums/s-class-w...ml#post9100828

 

Thanks. I have a friend that has a 2012 S550 and he's had to replace his main battery every 2-3 years. He has the AGM one for the car and we trying to figure out why it doesn't last and thought maybe the inner dash battery could be making the main battery drain.

 

you can't leave modern cars of any brand without battery support for more then 2 weeks at a time... and in some weird world they all seem to use more as they age - it might be as its less and less the daily driver, the time interval between starts increases without owners realising - but its certainly not just an ageing battery...

then of course the issue tends to be more prevalent on Mercs than other brands as they age - whether its damp soggy canbus networks keeping stuff alive and or draining away power for fun, or aged modules who's circuit boards magically leach power on purpose - few bother to hunt it down - as its easier and cheaper to put on charge and or just drive it every week

don't forget its likely a bit of everything alongside modern batteries that don't get made as well as they used to

her focus could do 2 months through winter without being touched during covid - and start as if it was the next day - but that’s not normal - in last 20 years one GM car I had could just manage 22 days and start - the newer one couldn't do 18 days, and the family have one e class that complains within 9 days (even when it has a new battery)

 

Google "w221 auxiliary battery" you will see and youtubers show how to relpace it

 

In my 2010 E550 the aux battery is a small fist size battery inside the driver’s side end if the dash and I think my 2012 S550 has the same and in same location. It is nowhere near the size of a motorcycle battery.

 

My first motorcycle was a Honda 50 in 1968 and it had the tiniest little battery.

 

bike one have shrunk now with lithium things (in size and weight)