Dual Battery Replacement
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Junior Member
Joined: May 2023
Posts: 15
Likes: 2
From: Dublin, Ohio USA
2020 S560
Dual Battery Replacement
I was been getting messages that my main battery on my 2020 S560 was low. I don’t drive it a lot (maybe 5K miles a year), and I had the dealer test both batteries. Sure enough, the main battery had problems, but the auxiliary battery was fine. So, the dealer replaced the main battery.
The next day, a new warning popped up: the auxiliary battery malfunctioned. I assumed something had not been properly reset, and I brought it back a day later. This time, they told me the auxiliary battery was bad and needed to be replaced.
So, I’m wondering whether this has happened to anyone else. Seems wrong that the auxiliary battery passed its test on one day, then failed after the main battery was replaced. How common is this? Anybody else have a similar experience? Thanks.
The next day, a new warning popped up: the auxiliary battery malfunctioned. I assumed something had not been properly reset, and I brought it back a day later. This time, they told me the auxiliary battery was bad and needed to be replaced.
So, I’m wondering whether this has happened to anyone else. Seems wrong that the auxiliary battery passed its test on one day, then failed after the main battery was replaced. How common is this? Anybody else have a similar experience? Thanks.
Super Member
Joined: Oct 2011
Posts: 697
Likes: 238
From: Illinois
S560/SL550/LS460/Q70L 5.6 AWD
If you're not comfortable to replace it (very easy) let them do it. If the warning comes back they are responsible to take care of it.
If in the future you will still drive the car for only 5K a year then you should use a battery tender, preferably a MB one, when the car is not being driven.
Just my O2 !
If in the future you will still drive the car for only 5K a year then you should use a battery tender, preferably a MB one, when the car is not being driven.
Just my O2 !
MBWorld Fanatic!
Joined: Feb 2012
Posts: 2,641
Likes: 1,224
From: Phoenix
222 S-65
They rarely live five years here in the desert.
There isn’t anything the dealership could do to the aux battery if they wanted to. It is common for a battery to test fine one day and be junk the next.
There isn’t anything the dealership could do to the aux battery if they wanted to. It is common for a battery to test fine one day and be junk the next.
Last edited by JohnLane; Feb 7, 2026 at 09:26 PM.
Super Member
Joined: Mar 2019
Posts: 573
Likes: 179
From: Half Moon Bay, CA
2016 S550e, 2005 Nissan Xterra 4x4, 1984 300ZX
PHX eats batteries! I lived there for 3 years (in the late 80s early 90s) and I got a new Interstate Battery every year! My Aux needed replacement after 6 years and main was just replaced (made it 8 years). They are no super straightfoward to replace, my mechanic showed me where it was in trunk and it took him 15 minutes to get in there, woudl have taken me a lot longer.
MBWorld Fanatic!
Joined: Dec 2011
Posts: 4,379
Likes: 952
W212 FL
I know some Mercedes-Benz Owners had their battery replaced beyond 5 years as well. Probably, if you can , CTEK would be a good choice to extend battery life if the car not is not been driven a lot . 5 Years is a fair life span to me , you would probably need a way earlier replacement in other car brands
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Junior Member
Joined: Mar 2013
Posts: 45
Likes: 6
2007 cls 63
Aux battery replacemtn
The auxiliary battery is pretty easy to replace. I purchased this one from FC P euro in the hopes that it has lifetime warranty.
https://www.fcpeuro.com/products/mer...a-205905341480
the trunk liner is just a few push pins - here is my video of the battery replacement -
doesn’t need coding
https://www.fcpeuro.com/products/mer...a-205905341480
the trunk liner is just a few push pins - here is my video of the battery replacement -
doesn’t need coding
Last edited by yagey; Feb 8, 2026 at 09:01 AM.
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Joined: Sep 2019
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From: U.S.
Current/Last 5-years:GLS;G70;Alpina B8;X7;Accord. Sold:X7,TeslaS;S560;S550,X5;530e;L.Navigator;LS460
The auxiliary battery is pretty easy to replace. I purchased this one from FC P euro in the hopes that it has lifetime warranty.
https://www.fcpeuro.com/products/mer...a-205905341480
the trunk liner is just a few push pins - here is my video of the battery replacement -
doesn’t need coding
https://youtu.be/VeLzEALj_EQ?si=Jo2Vn3O1wlCdRaXV
https://www.fcpeuro.com/products/mer...a-205905341480
the trunk liner is just a few push pins - here is my video of the battery replacement -
doesn’t need coding
https://youtu.be/VeLzEALj_EQ?si=Jo2Vn3O1wlCdRaXV
