Small access opening to negative terminal to trunk 12V battery
Thread Starter
Member
Joined: May 2024
Posts: 85
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S-class, E450 W214, E350 W214
Small access opening to negative terminal to trunk 12V battery
Underneath the trunk floor covering, there is a small opening that can be used to gain access (held closed by a cover with velco strap) to the negative terminal of the 12V battery in the trunk. However, since only the negative (but not the positive) terminal is exposed by opening this small cover, this cannot be used to directly or trickle charge the battery. Does anyone know what is the intended purpose of this opening?
Also, the reason I happen to stumble on this is that I am trying to attach a pair of permanent charging wires directly to the battery for easier trickle charging. Would really appreciate If anyone has some instructions on how to remove the trim coverings in the trunk to gain access to the battery terminal (on my S-class, the trim coverings are held together by screws and tabs but seemingly not in my 2025 E450).
Also, the reason I happen to stumble on this is that I am trying to attach a pair of permanent charging wires directly to the battery for easier trickle charging. Would really appreciate If anyone has some instructions on how to remove the trim coverings in the trunk to gain access to the battery terminal (on my S-class, the trim coverings are held together by screws and tabs but seemingly not in my 2025 E450).
Junior Member
Joined: Mar 2024
Posts: 34
Likes: 1
2024 E450
I also wanted to connect permanent trickle charger cables to the battery in the trunk and didn’t know how to connect to the positive terminal of the battery since it’s covered.I brought my car to Mercedes Service and asked one of the technicians to show me what to do. Actually, you just have to pull in the edges of the cover from the sides of the trunk and it will pop up.There was some kind of an attachment to the positive terminal of the battery that the mechanic actually had to take it off the battery terminal in order to connect the charger cable to it.The negative charger cable needs to be connected to the ground screw in the back top of the trunk and not to the negative terminal of the battery, which will otherwise give you a message that the batteries is being discharged.FThe problem was that after my mechanic took the positive car cable off the positive terminal and then reconnected, the car check engine light went on, and he had to reset all the faults and after that it was fine, but I wouldn’t do it myself and I’m happy I didn’t.I hope this helps.
MBWorld Fanatic!
Joined: Jul 2013
Posts: 4,834
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From: Venice Florida
2018 S560
There must be thermals to connect the battery maintainer under the hood like there always been? If not mb screwed up? I still haven’t looked at my 2025 all terrain under the hood.
Thread Starter
Member
Joined: May 2024
Posts: 85
Likes: 32
S-class, E450 W214, E350 W214
I also wanted to connect permanent trickle charger cables to the battery in the trunk and didn’t know how to connect to the positive terminal of the battery since it’s covered.I brought my car to Mercedes Service and asked one of the technicians to show me what to do. Actually, you just have to pull in the edges of the cover from the sides of the trunk and it will pop up.There was some kind of an attachment to the positive terminal of the battery that the mechanic actually had to take it off the battery terminal in order to connect the charger cable to it.The negative charger cable needs to be connected to the ground screw in the back top of the trunk and not to the negative terminal of the battery, which will otherwise give you a message that the batteries is being discharged.FThe problem was that after my mechanic took the positive car cable off the positive terminal and then reconnected, the car check engine light went on, and he had to reset all the faults and after that it was fine, but I wouldn’t do it myself and I’m happy I didn’t.I hope this helps.
Junior Member
Joined: Mar 2024
Posts: 34
Likes: 1
2024 E450
Thanks so much for your info. That would explain why there are no screws or tabs that would hold down the truck cover like in my S-class. I do not know whether your Mercedes tech did this or not, but it is advisable to hook up an external power source to avoid computer memory issues when detaching the positive terminal of the main battery and may be that is the cause of the check engine light being triggered. I will attempt to attach the trickle charger cables permanently to the trunk battery later and will share my experiences afterwards in this forum.
