Changing Main Battery
Thread Starter
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Joined: Nov 2025
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2018 Fiat 124 Spider, 2019 MB C300
Changing Main Battery
I own a 2019 C300 Sedan and it is time to change the main battery. I know how to do the mechanical part,
but what do I need to do to keep the car's electronics happy? (reset Battery counter?, reset / restore other settings ?)
... and how would I do these things? Do I need a compatible OBDII-scanner?
Thanks so much for any advice and help.
Trombone77
but what do I need to do to keep the car's electronics happy? (reset Battery counter?, reset / restore other settings ?)
... and how would I do these things? Do I need a compatible OBDII-scanner?
Thanks so much for any advice and help.
Trombone77
MBWorld Fanatic!
Joined: Oct 2019
Posts: 5,193
Likes: 1,783
From: Colorado
G550
If you're speaking about keeping the car powered during the battery swap so that a bunch of functions such as radio presets and windows don't flake out, I use a Noco charger set to 12V and the accessory OBD connector power adapter. Alternately you can clamp a small 12V battery onto the battery clamps, but that can be awkward trying to keep it connected while keeping the cables out of the way while swapping batteries.
Junior Member
Joined: Aug 2019
Posts: 51
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2018 C300 Sedan
I own a 2019 C300 Sedan and it is time to change the main battery. I know how to do the mechanical part,
but what do I need to do to keep the car's electronics happy? (reset Battery counter?, reset / restore other settings ?)
... and how would I do these things? Do I need a compatible OBDII-scanner?
Thanks so much for any advice and help.
Trombone77
but what do I need to do to keep the car's electronics happy? (reset Battery counter?, reset / restore other settings ?)
... and how would I do these things? Do I need a compatible OBDII-scanner?
Thanks so much for any advice and help.
Trombone77
Thread Starter
Newbie
Joined: Nov 2025
Posts: 4
Likes: 0
2018 Fiat 124 Spider, 2019 MB C300
I read somewhere, that the C300 adjusts the charging voltage depending on the age (internal resistance)
of the battery. More voltage and more charging current when the battery is older. Thus, unless a new
battery is registered with the board computer, the charging current might be larger than necessary and
wear out the battery faster. Is this just nit-picky or a real concern?
Also, can somebody suggest a suitable OBDII scanner for these cars? I only have a basic device that
doesn't seem to be able to do the trick.
Thanks again,
trombone 77
MBWorld God!
Joined: Dec 2019
Posts: 32,673
Likes: 6,419
Thank you very much, everybody, for the valuable responses.
I read somewhere, that the C300 adjusts the charging voltage depending on the age (internal resistance)
of the battery. More voltage and more charging current when the battery is older. Thus, unless a new
battery is registered with the board computer, the charging current might be larger than necessary and
wear out the battery faster. Is this just nit-picky or a real concern?
Also, can somebody suggest a suitable OBDII scanner for these cars? I only have a basic device that
doesn't seem to be able to do the trick.
Thanks again,
trombone 77
I read somewhere, that the C300 adjusts the charging voltage depending on the age (internal resistance)
of the battery. More voltage and more charging current when the battery is older. Thus, unless a new
battery is registered with the board computer, the charging current might be larger than necessary and
wear out the battery faster. Is this just nit-picky or a real concern?
Also, can somebody suggest a suitable OBDII scanner for these cars? I only have a basic device that
doesn't seem to be able to do the trick.
Thanks again,
trombone 77
I want to add Launch CReader Elite Benz V2.0 has something called a BBA version which apparently stands for Benz BMW Audi, it is around the same cost or just a few dollars more, it also has physical navigation buttons. So that is a good option as well for those who have other models or just want to have physical buttons.
Furthermore, you can still purchase (subscription) the 3 German brands from the app store on the regular Launch CReader Elite Benz V2.0 but it will always be more expensive than all 3 brands built-in purchased once.
Discussion on this scanner linked:
https://mbworld.org/forums/coupe-roa...tc-2018-a.html
https://mbworld.org/forums/glc-class-x254/926639-75-scan-tool-choice-glc300.htm
I am not sure if you really should buy this scanner just for one time use like registering the battery unless you find use for it somehow.
Last edited by W205C43PFL; May 6, 2026 at 04:45 PM.
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The state of charge system adjusts the alternator input dynamically. I don't know that it does this in relation to the battery's age -- can anyone actually confirm that? I've never used the OBDII to re-set mine.
Some data points that might be useful to people who read this thread: If you disconnect the state of charge system (at the negative battery plug) two things happen. It goes to a straight 14.1 charge always (like many other cars do), and it disables the Eco Start/Stop feature. I often leave the state of charge plug disconnected in order to not be bothered by the Eco Start/Stop nonsense. In 10 years of ownership, I have not seen an effective difference in having the charging be a constant 14.1, rather than going between 13.4 and 14.8. I've gotten ~5 years out of each battery and do a crazy amount of in-town driving. The car is now approaching 140,000 miles.
Some data points that might be useful to people who read this thread: If you disconnect the state of charge system (at the negative battery plug) two things happen. It goes to a straight 14.1 charge always (like many other cars do), and it disables the Eco Start/Stop feature. I often leave the state of charge plug disconnected in order to not be bothered by the Eco Start/Stop nonsense. In 10 years of ownership, I have not seen an effective difference in having the charging be a constant 14.1, rather than going between 13.4 and 14.8. I've gotten ~5 years out of each battery and do a crazy amount of in-town driving. The car is now approaching 140,000 miles.
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MBWorld Fanatic!
Joined: Oct 2019
Posts: 5,193
Likes: 1,783
From: Colorado
G550
The state of charge system adjusts the alternator input dynamically. I don't know that it does this in relation to the battery's age -- can anyone actually confirm that? I've never used the OBDII to re-set mine.
Some data points that might be useful to people who read this thread: If you disconnect the state of charge system (at the negative battery plug) two things happen. It goes to a straight 14.1 charge always (like many other cars do), and it disables the Eco Start/Stop feature. I often leave the state of charge plug disconnected in order to not be bothered by the Eco Start/Stop nonsense. In 10 years of ownership, I have not seen an effective difference in having the charging be a constant 14.1, rather than going between 13.4 and 14.8. I've gotten ~5 years out of each battery and do a crazy amount of in-town driving. The car is now approaching 140,000 miles.
Some data points that might be useful to people who read this thread: If you disconnect the state of charge system (at the negative battery plug) two things happen. It goes to a straight 14.1 charge always (like many other cars do), and it disables the Eco Start/Stop feature. I often leave the state of charge plug disconnected in order to not be bothered by the Eco Start/Stop nonsense. In 10 years of ownership, I have not seen an effective difference in having the charging be a constant 14.1, rather than going between 13.4 and 14.8. I've gotten ~5 years out of each battery and do a crazy amount of in-town driving. The car is now approaching 140,000 miles.
