SL/R231: OEM Battery life
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From: Hagerstown MD
2015 SL400; 2019 X5M40i
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ML350
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From: Hagerstown MD
2015 SL400; 2019 X5M40i
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From: Philadelphia area
2014 SL65 AMG, 2018 S560
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From: Maryland
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
To remove the cage, lift and remove the rear storage with the sliding door. It comes right off. you may need to tilt the forward part up. Then carefully unclip the trim that attaches to the center console by pulling it away from the console FROM THE MIDDLE of the trim and NOT the end. It is flexible. Once detached, just move it out of the way enough to get the cage out. Reverse the process to get everything back in place.
Seach YouTube for how to remove the center console trim.
Last edited by JettaRed; May 17, 2025 at 08:44 AM.
Joined: Nov 2016
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From: Maryland
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
More generally, the Aux battery's purpose is to enable the ECO Start/Stop for work. It apparently provides power to the external transmission fluid pump so that the tranny is presurized to be ready when the car starts up again. ECO Start/Stop is stupid and damaging. It was never mandatory in the US, but intended to hit mileage targets mandated by the EPA. The EPA doesn't care if it's rules damage your car.
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From: Nothern Georgia, U.S.A.
'17 SL450, '25 Lyriq, '25 Sonata Hybrid, '96 Corvette GS coupe
The Aux battery also powers the keyless entry system receiver when the car is off/locked. I've never had any problem with the way the start/stop system works, which is flawlessly. I don't drive the car much, so it's not really saving me much money, but the potential for reducing emissions is real if all cars are using a similar system. I may be the lone ranger here for caring about such things, but I can't help it.
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From: Central Florida
'13 SL550 Mars Red, Designo White interior, B and O sound
Aux Battery Installation: cutting plastic frame.
Bit late to this but, yes, I did make a couple of cuts. No biggy.
Last edited by Bitbytr; Jul 19, 2025 at 10:41 AM. Reason: Reply not attached to original question therefore utterly out of context
Member
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From: Central Florida
'13 SL550 Mars Red, Designo White interior, B and O sound
The Aux battery also powers the keyless entry system receiver when the car is off/locked. I've never had any problem with the way the start/stop system works, which is flawlessly. I don't drive the car much, so it's not really saving me much money, but the potential for reducing emissions is real if all cars are using a similar system. I may be the lone ranger here for caring about such things, but I can't help it.
Super Member
Joined: Jul 2018
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From: Nothern Georgia, U.S.A.
'17 SL450, '25 Lyriq, '25 Sonata Hybrid, '96 Corvette GS coupe
Member
Joined: Feb 2014
Posts: 152
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From: Central Florida
'13 SL550 Mars Red, Designo White interior, B and O sound
Not aimed at you for sure just an observation and apologies if that wasn't clear. It's just that I fail to understand why it is a "stupid" and "damaging" function when it can–and does–save emissions, a little gas and hasn't been proven damaging except to those whose feelings are hurt by "gummint" intervention for the greater good. Now, if it interferes with one's desperate need for instant acceleration from that ol' red light in town, turn it off: the button's right there next to the tranny (oops: there's another controversy brewing LOL) shift-pattern selection button. No biggy ... certainly not a political issue.
Is it?
Is it?
Super Member
Joined: Jul 2018
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From: Nothern Georgia, U.S.A.
'17 SL450, '25 Lyriq, '25 Sonata Hybrid, '96 Corvette GS coupe
Not aimed at you for sure just an observation and apologies if that wasn't clear. It's just that I fail to understand why it is a "stupid" and "damaging" function when it can–and does–save emissions, a little gas and hasn't been proven damaging except to those whose feelings are hurt by "gummint" intervention for the greater good. Now, if it interferes with one's desperate need for instant acceleration from that ol' red light in town, turn it off: the button's right there next to the tranny (oops: there's another controversy brewing LOL) shift-pattern selection button. No biggy ... certainly not a political issue.
Is it?
Is it?
Newbie
Joined: Oct 2023
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2017 SL450
As a followup, I used this OBDII scanner to check the condition of my main battery directly from it's terminals in the trunk. The date code on the negative post is 51/16. I think I'm good based on this. Does anyone have more experience with this type of diagnostic, to where I shouldn't be so confident?
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From: Nor-Cal
2020 GLC300 -2014 Sl550 - 1997 SL600
As a followup, I used this OBDII scanner to check the condition of my main battery directly from it's terminals in the trunk. The date code on the negative post is 51/16. I think I'm good based on this. Does anyone have more experience with this type of diagnostic, to where I shouldn't be so confident?
You should have the battery either load tested or resistance tested. Voltage isn’t always an indicator of a healthy AGM battery.
it can easily read 12 volts and still be weak cranking amperage wise….
here’s some battery info
https://mbworld.org/forums/sl-class-...ent-guide.html
MB battery conductance tester
https://mbworld.org/forums/sl-class-...ml#post8608015
Good Luck
Last edited by crconsulting; Jul 29, 2025 at 09:18 AM.
Newbie
Joined: Oct 2023
Posts: 12
Likes: 2
2017 SL450
You should have the battery either load tested or resistance tested. Voltage isn’t always an indicator of a healthy AGM battery.
it can easily read 12 volts and still be weak cranking amperage wise….
here’s some battery info
https://mbworld.org/forums/sl-class-...ent-guide.html
MB battery conductance tester
https://mbworld.org/forums/sl-class-...ml#post8608015
Good Luck
it can easily read 12 volts and still be weak cranking amperage wise….
here’s some battery info
https://mbworld.org/forums/sl-class-...ent-guide.html
MB battery conductance tester
https://mbworld.org/forums/sl-class-...ml#post8608015
Good Luck
Great info, thanks!
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Joined: Dec 2015
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From: Hagerstown MD
2015 SL400; 2019 X5M40i
Here is a source for the auxiliary battery.
Mercedes Auxiliary Battery - Genuine Mercedes 0009829608 | FCP Euro https://share.google/ZfBn2Uc7wwhG85LQ9
I was able to replace mine so installation isn't too difficult.
Mercedes Auxiliary Battery - Genuine Mercedes 0009829608 | FCP Euro https://share.google/ZfBn2Uc7wwhG85LQ9
I was able to replace mine so installation isn't too difficult.
Last edited by rmorin49; Jul 30, 2025 at 09:13 AM.
