SL/R231: Battery Maintainer
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Joined: Dec 2015
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From: Hagerstown MD
2015 SL400; 2019 X5M40i
Battery Maintainer
I used a CTEK Battery Maintainer on my Corvette when it wasn't driven for a week or more. I plan to use it on our SL as well. Does anyone know if it will keep both batteries properly charged if the cables are connected to the terminals in the engine compartment?
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Same effect as connecting directly to the main battery in the trunk.
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From: Illinois
S560/SL550/LS460/Q70L 5.6 AWD
If it is like in the previous model, then I would connect the CTEK to the main battery. The R230 had a starting battery in the engine compartment, if that one was low on power then the car was switching to the one in the trunk. I have always stored the car during the winter and used the CTEK connected to the main battery in the trunk, I hope this helps.
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From: Hagerstown MD
2015 SL400; 2019 X5M40i
Thanks. I'm going to ask a knowledgeable tech at my local MB dealer. I'm thinking that maybe the secondary battery might be responsible for opening and closing the roof. Sound plausible?
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If it is like in the previous model, then I would connect the CTEK to the main battery. The R230 had a starting battery in the engine compartment, if that one was low on power then the car was switching to the one in the trunk. I have always stored the car during the winter and used the CTEK connected to the main battery in the trunk, I hope this helps.
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Only MBs - the best or nothing
No, second battery is responsible for, relatively speaking, minor functions like "hold", tpms plus few others. Starting, roof and all other main functions are performed by the main battery. One can not connect to (or at least its hard) aux battery in R231 because its a huge pain to get to (I tried, then took car to the dealer to replace aux battery).
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Thread Starter
MBWorld Fanatic!
Joined: Dec 2015
Posts: 1,635
Likes: 521
From: Hagerstown MD
2015 SL400; 2019 X5M40i
Did a google search and watched a couple YouTube videos. Seems the "convenience" battery located behind the passenger seat may be on a separate circuit and thus would NOT be maintained by a maintainer connected to the main battery terminals under the hood. This is too bad as I agree it is a major pain to connect a maintainer to the other battery behind the passenger seat. I'm guessing these batteries are probably not good for more than 5 years so I will be looking into replacing mine in a year or so assuming my car, a 2015, still has the original batteries. Appreciate the feedback.
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Joined: Jul 2019
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From: Rhode Island
2013 SL550, 2017 GLE350, 2018 Audi Q3
That is one thing I asked the dealership regarding my SL550...what is the age of the main and convenience batteries? I haven't got an answer back from them.
Because the convenience battery is a pain to get to, I may make up a wiring harness to bring out a connection to a plug so I can easily connect it to a charger.
Because the convenience battery is a pain to get to, I may make up a wiring harness to bring out a connection to a plug so I can easily connect it to a charger.
