SL/R231: Battery Saver for auxiliary battery

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Apr 10, 2023 | 07:38 AM

SLDOUG

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Junior Member

Joined: Apr 2021

Posts: 71

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From: Canada

2013 SL 550 R231

Battery Saver for auxiliary battery

I am Looking to change my auxiliary battery (The one behind passenger seat) on my SL550

Do I need to install a battery saver as you do for the main battery to protect all memories and settings

Thank you,
Regards
SLDoug

Apr 10, 2023 | 10:37 AM

crconsulting

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Joined: Feb 2021

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From: Nor-Cal

2020 GLC300 -2014 Sl550 - 1997 SL600

Quote:

Originally Posted by SLDOUG

I am Looking to change my auxiliary battery (The one behind passenger seat) on my SL550
Do I need to install a battery saver as you do for the main battery to protect all memories and settings

It is recommended by MB that you disconnect the negative terminal on your MAIN battery before replacing the auxiliary battery. So you probably will want a memory saver device if you wish to preserve your preset's.

Apr 10, 2023 | 11:33 AM

SLDOUG

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Junior Member

Joined: Apr 2021

Posts: 71

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From: Canada

2013 SL 550 R231

Thank you for the info
Regards
SLDoug

Sep 29, 2025 | 04:42 PM

andy-gts

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Joined: Sep 2019

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sl63 amg

just changed mine , didnt disconnect the main battery, all is well, no electronic gremlins...2014 sl63

Sep 29, 2025 | 05:56 PM

crconsulting

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From: Nor-Cal

2020 GLC300 -2014 Sl550 - 1997 SL600

Quote:

Originally Posted by andy-gts

just changed mine , didnt disconnect the main battery, all is well, no electronic gremlins...2014 sl63

Excellent, for what it’s worth, the WIS for the R231 Aux Battery Removal (see attached) specifically doesn’t mention disconnecting the main battery. But MB’s latest “blanket” recommendation is based on how different BCM’s are very different from model to model. Some WIS specify disconnecting the main battery, some don’t. Some BCM’s have to also be reset. If I was working on someone else’s car, I would disconnect it out of precaution.

Luckily, the R231 BCM is relatively simple, and disconnect's when it’s not being charged and off.

Good Luck

Attached Files

Remove_install additional battery_01.pdf (139.6 KB, 161 views)

Last edited by crconsulting; Sep 29, 2025 at 06:07 PM.

Sep 30, 2025 | 08:04 AM

jmattioni

Senior Member

Joined: Jan 2019

Posts: 474

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From: Philadelphia area

2014 SL65 AMG, 2018 S560

Another interesting tidbit is that you don't need to put a memory saver on the R231 when changing the main battery. I have disconnected the main battery negative terminal many times on my 2014 SL for days while working on it and have not lost any settings.

Sep 30, 2025 | 08:58 AM

JettaRed

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From: Maryland

2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)

Quote:

Originally Posted by jmattioni

Not to mention a complete disconnect of both batteries help reset some stored parameters that may be causing "problems". I'm not really sure which settings might be affected that don't relearn everything after a few hundred miles. The only thing I can think of is maybe the anti-pinch settings for the automatic windows. But that is easy enough to fix.