Battery replacement for 2010+ W221. Does a 12v source need to stay connected???
Thread Starter
MBWorld Fanatic!
Joined: Dec 2001
Posts: 3,430
Likes: 187
From: USA
W140 Mercedes S350, W221 S550 sport
Battery replacement for 2010+ W221. Does a 12v source need to stay connected???
Battery replacement for 2010+ W221. Does a 12v source need to stay connected before removing the old battery? Or can you disconnect it and be fine with losing power???
MBWorld Fanatic!
Joined: Nov 2014
Posts: 1,560
Likes: 207
From: Maryland
Depends on the weather
You could do it either way but the right way is with the 12v source. There is a lot of computers on these cars and that way you keep all of them online and no reseting afterwards.
MBWorld Fanatic!
Joined: Nov 2014
Posts: 1,560
Likes: 207
From: Maryland
Depends on the weather
Strange, I didn't have to reset anything when I disconnected mine. I've done it twice in 2 different cars for ECU and TCU tunes and sent them out to be tuned and back and it was disconnected for a few days.
Last edited by WHPH28; Apr 6, 2021 at 07:19 PM.
Senior Member
Joined: Nov 2002
Posts: 303
Likes: 25
2013 - with the single big battery - didn't have to provide power during the change over - and I had it disconnected for about 15 minutes. No settings or normalizations were lost in the process. I suspect the *little* battery under the dash provides some continuity.
MBWorld Fanatic!
Joined: Nov 2014
Posts: 1,560
Likes: 207
From: Maryland
Depends on the weather
Yup, the auxillary battery on the drivers side in the dash, left of the steering wheel.
MBWorld Fanatic!
Joined: Oct 2010
Posts: 5,141
Likes: 1,293
From: Southern US
2010 E550, 273 Engine: 2012 S550, 278 Engine
If you ever decide to use some sort of power during battery change make sure you use battery powered device. Some battery chargers do not give perfectly clean DC power, which even at low voltage can be very harmful.
Also, once I had my battery changed on my E550 at AutoZone and they used some power box connected to the OBD socket. Result was it burned the fuse of the OBD socket.
Trending Topics
MBWorld Fanatic!
Joined: Aug 2014
Posts: 5,317
Likes: 1,673
S500
the W220 had to give support when disconnecting the battery, normal later cars don't
the Aux battery is a muddled name on Mercs, for anything post 2008 the Aux battery is the start stop logic / systems support battery.... before that it was the emergency brake servo assistance battery for one's with SBC
Then on some early W221s you has a consumer toys battery in the boot and the smaller starter battery in the front, not to be confused with a low volt main battery and consumer toys disabled message on the W211
one day they will make cars like normal manufacturers that just work
the Aux battery is a muddled name on Mercs, for anything post 2008 the Aux battery is the start stop logic / systems support battery.... before that it was the emergency brake servo assistance battery for one's with SBC
Then on some early W221s you has a consumer toys battery in the boot and the smaller starter battery in the front, not to be confused with a low volt main battery and consumer toys disabled message on the W211
one day they will make cars like normal manufacturers that just work
MB World Stories
The Best of Mercedes & AMG
Manual Mercedes? 6 Times Sindelfingen Let Drivers Have All The Fun
Verdad Gallardo
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Verdad Gallardo
8 Classic Boxy Mercedes Designs That Have Aged Like Fine Wine
Verdad Gallardo
Flawlessly Restored Mercedes 190E Evo II Heads to Auction
Verdad Gallardo
Electric Mercedes C-Class Unveiled: 11 Things You Need to Know
Verdad Gallardo
Mercedes EQS Gets A Major Update: Everything You Need to Know
Verdad Gallardo
5 Underrated Mercedes-Benz Models That Don't Get the Love They Deserve
Verdad Gallardo
Mercedes 300D Has Pushed Well Past 1 Million Miles and It Ain't Stopping
Verdad Gallardo
