AMG GT63S electrical problem
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2020 Mercedes AMG GT63S
AMG GT63S electrical problem
Hello I have a 2020 63s 4d sedan and I’ve been having an issue over the past year where sometimes my car won’t start not even with a jump but if I walk away and come back 10 minutes later it starts up no problem and I’ve taken it in multiple times so far and this past time they’re telling me I need a new battery which is $3200. Has anyone else had this issues as well?
On a side note they’re also telling me I have 2 batteries and main starter one is on the trunk and I’ve checked and there’s an air compressor in the trunk and no battery, just the one under the hood so am I missing anything?
On a side note they’re also telling me I have 2 batteries and main starter one is on the trunk and I’ve checked and there’s an air compressor in the trunk and no battery, just the one under the hood so am I missing anything?
Last edited by FUGAZY; Mar 18, 2026 at 09:51 PM.
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2019 C63CS
The main battery is an AGM battery in the GT 4-door as far as I remember. Those last 4-6 years, so given the age of your car, it's likely toast. They are also correct that there's a second battery. It's called the auxiliary battery and is there to stabilize the voltage for the electronics during an engine start and assist with ECO start/stop. In some models it's not actually a battery, but a capacitor. Either way, it's recommended to replace it at the same time that main battery is replaced. In the GT it's indeed in the trunk as far as I remember. Right side I believe behind the sidewall, so it takes a bit of disassembly to get to it. However, $3200 is quite the highway robbery. I paid less than $500 to replace the main AGM battery in my C63S Coupe at the dealership. It's in the same place and easily accessible. It's a 1/2 hour job. I ended up replacing the aux battery myself. In my case it's behind the passenger side footwell panel. The module itself was like $120 through FCP Euro and it's supposed to be a 15 minute job. Took me about an hour following the instructions from a YouTube video and figuring out how much I can pull on the panels w/o breaking anything, so first time takes a bit longer. Taking the trunk trim off isn't all that much more work. In fact it might be easier as working down in the footwell isn't particularly convenient. So, if they want $3200 for this, they are putting somebody through college on your dime.
Last edited by superswiss; Mar 18, 2026 at 09:15 PM.
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2020 Mercedes AMG GT63S
It definitely is crazy
The GT63s has this lithium-ion battery which they tell me needs to be programmed after being installed and they’re telling me the auxiliary battery is an H9 AGM battery but who knows. The battery under the hood says on it LIT-ION so I’m assuming that’s the main starter battery. The issue I’m having doesn’t make sense that it’s the battery bc if it’s a dead battery then the car shouldn’t start unless it gets a jump but with me it starts up after some time when it’s not connected to a jump box
Last edited by FUGAZY; Mar 18, 2026 at 09:53 PM.
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2019 C63CS
Ah ok, the GT 4-door does have a lithium battery. So yeah those are pricier. When the battery gets faulty, you can have all kinds of weird issues that may not make sense.
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2019 C63CS
Here are aux battery options. Less than $300 for the battery, but it's an aftermarket battery. You'll be at $2000 in parts, so $1200 for labor is still insane.
https://www.fcpeuro.com/Mercedes~Ben...atic&year=2020
https://www.fcpeuro.com/Mercedes~Ben...atic&year=2020
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2020 Mercedes AMG GT63S
Definitely Crazy!!
The OEM auxiliary battery is under $300. The $3,200 quote from Mercedes is just for the main Lithium battery ($2400) and $600 in labor and then CA tax which comes out to 200 and change. I’m not disputing that the battery has to be changed at some point but this problem I’ve been having over the past year doesn’t seem to me to be a battery related issue if every 2 months or so the car won’t start but if I walk away and then come back 10 minutes later it starts up with no issue
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2001 S600 V12 Sold, 2011 Jaguar XFR Sold, 2017 S550 4-Matic, 2018 S63 AMG Sedan
The OEM auxiliary battery is under $300. The $3,200 quote from Mercedes is just for the main Lithium battery ($2400) and $600 in labor and then CA tax which comes out to 200 and change. I’m not disputing that the battery has to be changed at some point but this problem I’ve been having over the past year doesn’t seem to me to be a battery related issue if every 2 months or so the car won’t start but if I walk away and then come back 10 minutes later it starts up with no issue
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2020 Mercedes AMG GT63S
Thanx
I have not replaced the battery and the car has kept its charge without any issues so far and I’ll look into that because that actually makes sense to me with the issues I’ve been having thank you. Now I just have to convince the service techs to take a look at bc I have a warranty through Mercedes or find a new MB dealership to go to
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