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when I acquired the car a month ago, the instrument cluster showed "change key fob battery". So I changed the key fob battery. I didnt drive the car that much, maybe a dozen times. 3 weeks later, the message showed up again?!. I read somewhere on the forum people mentioned using the key fob to open/close the car's door will clear/fix that message.... that didnt work for me. Changing battery every 3-4 weeks doesnt seem very normal to me. Anybody know how to fix this? what might be the cause?
I had a pack of batteries that didn't last very long a while back. Just a few months (6-8?) in the fob. Did it in two different cars from different manufacturers at the same time though, so I only suspected the car for a week or so. They were name brand, and I suspected possibly fakes or something, but it seems an odd thing to try to fake. Next batch of batteries has been going a more normal duration.
Keyless go cars use a smaller battery and leaving the key too close to the car wears out the batteries quickly, you may have gotten old batteries as others suggested, my batteries last twice as long if I keep the key out of range of the car and in a metal dish
when I acquired the car a month ago, the instrument cluster showed "change key fob battery". So I changed the key fob battery. I didnt drive the car that much, maybe a dozen times. 3 weeks later, the message showed up again?!. I read somewhere on the forum people mentioned using the key fob to open/close the car's door will clear/fix that message.... that didnt work for me. Changing battery every 3-4 weeks doesnt seem very normal to me. Anybody know how to fix this? what might be the cause?
Your Mercedes has multiple items that require care services.
Obviously use new fob batteries... I bet you knew that.
What drains both car and fob batteries is when the car keep polling it's security lock devices. To prevent that busy work: LOCK your car even at home.
> Drain fob battery has a root cause:
new battery every month is not a fix but a bandaid.
The next step requires to sanitize the unstable CAN-B Modules starting with:
a full OBD scan
reboot
cleaning GND and
soldering poor connections
Then your fob battery will last forever like 2, 3 or more years and doors/trunk will unlock reliably like any Japanese car.
Chinese Mercedes: a "C260 L" ... Long-base Compact !
Last edited by CaliBenzDriver; Nov 17, 2025 at 10:11 AM.
My key fob went through the wash and I thought it was done for. After it dried out I tried it and it didn't work. Took the battery from my other fob and the washed fob worked perfect. MB must have good fob circuitry or I got lucky.
Keyless go cars use a smaller battery and leaving the key too close to the car wears out the batteries quickly, you may have gotten old batteries as others suggested, my batteries last twice as long if I keep the key out of range of the car and in a metal dish
Keyless go cars use a smaller battery and leaving the key too close to the car wears out the batteries quickly, you may have gotten old batteries as others suggested, my batteries last twice as long if I keep the key out of range of the car and in a metal dish
Yes, I forgot this. Good catch Pierre. I keep my car locked (even in the garage) to turn off most of the consumers. And, I store the fobs 60 feet away from the car to get them out of range.
I had a similar thing happened to me on my key fob as well. What I did was that I just swapped the battery and inserted into the other key fob then operated the fob . Then, the same battery went into the original one and operated pressing the buttons . No more battery related message . Fluke or not probably an erratic key fob , I just wanted to share my experience
I've went thought a bunch of batteries until I've took on @CaliBenzDriver advise and went from solderless to soldered keyless go module. Doing the battery reset works for about one month, but after soldering the solderless pins I can't even remember when was the last time I had to replace the FOB batteries. It's a very easy job, don't be intimidated by it.
I've went thought a bunch of batteries until I've took on @CaliBenzDriver advise and went from solderless to soldered Keyless-Go module.
Doing the battery reset works for about one month, but after soldering the solderless pins I can't even remember when was the last time I had to replace the FOB batteries.
It's a very easy job, don't be intimidated by it.
@Andre Cateb
Andre: now that you've seen how good a few simple steps can deliver chaos free operation - You realize our cars were engineered to deliver the Mercedes-Benz experience we've to expect.
Here is more simple-fun for the engine electronic control:
REBOOT chassis (Sanitize SAM-CGW!)
FLOAT main battery (minimize dropped voltage)
ALT-LIN stable chassis voltage (coils...)
not to mention effective oiling with MOD-X.
The whole chassis is extremely sensitive to voltage variations. May be great only up to 3 days... then you begin wondering what's up with CGW that's bugging the ECU-TCU.
What we're dealing with are not single items but a system of interconnected CAN Modules.
When the Keyless is bugging CAN-B with slow retransmits it impacts more than what we think it should.
Bosch CAN is not a perfect world of isolated traffic packets. Reduced busy-work shows experimental improvements. So more free goodies available after soldering.
MB E200: 2L 4Cyl. - Perfect for Hong-Kong heat...
Last edited by CaliBenzDriver; Nov 20, 2025 at 11:31 AM.
I've went thought a bunch of batteries until I've took on @CaliBenzDriver advise and went from solderless to soldered keyless go module. Doing the battery reset works for about one month, but after soldering the solderless pins I can't even remember when was the last time I had to replace the FOB batteries. It's a very easy job, don't be intimidated by it.
Hi, can you please post CaliBenzDriver original advice? Im willingly to try out... Thank you
I agree with everyone here regarding locking the car and storing the fob away from the vehicle. I can add the fob using a cr2025 battery, I recently installed a cr2032 which is slightly thicker but still fits in the fob and has lasted a lot longer than the cr2025
I agree with everyone here regarding locking the car and storing the fob away from the vehicle. I can add the fob using a cr2025 battery, I recently installed a cr2032 which is slightly thicker but still fits in the fob and has lasted a lot longer than the cr2025
Yes exactly!
Do install CR2032 instead of stock CR2025.
The coin cell seriously look like it was downgraded to be undersized. 2032 is still a great match.
Your Mercedes has multiple items that require care services.
Obviously use new fob batteries... I bet you knew that.
What drains both car and fob batteries is when the car keep polling it's security lock devices. To prevent that busy work: LOCK your car even at home.
> Drain fob battery has a root cause:
new battery every month is not a fix but a bandaid.
The next step requires to sanitize the unstable CAN-B Modules starting with:
a full OBD scan
reboot
cleaning GND and
soldering poor connections
Then your fob battery will last forever like 2, 3 or more years and doors/trunk will unlock reliably like any Japanese car.
Chinese Mercedes: a "C260 L" ... Long-base Compact !
Hi CaliBenz. I was busy sorting out the car step by step, plus the hectic holiday schedule.... Last week I was successfully turned on the Android Auto option on my car. Today I will start working on the key issue. I already replaced the key's battery (3 times), trickled charge the car (when not in use). I also scanned and cleared all the codes, rebooted. Locked and stored key far away from the car. So far all the steps I did didnt fix the "replace battery" issue. Today I will dig into solder the connections you mentioned.
Last edited by nguyenphananh; Dec 1, 2025 at 01:35 PM.
Hi CaliBenz. I was busy sorting out the car step by step, plus the hectic holiday schedule.... Last week I was successfully turned on the Android Auto option on my car. Today I will start working on the key issue. I already replaced the key's battery (3 times), trickled charge the car (when not in use). I also scanned and cleared all the codes, rebooted. Locked and stored key far away from the car. So far all the steps I did didnt fix the "replace battery" issue. Today I will dig into solder the connections you mentioned.
so you know, in Mercedes world you can have a perfectly good everything and still get "replace battery"...
Once you have installed new keyfob coin cell there is a procedure to clear the "replace battery" error screen.
so you know, in Mercedes world you can have a perfectly good everything and still get "replace battery"...
Once you have installed new keyfob coin cell there is a procedure to clear the "replace battery" error screen.
Search for that error message on youtube.
oh... that is new to me!. I just quick search google, the only procedure I found was to disconnect battery for 15 mins to reset or clear with scanner... am I corected? or is there any other procedure??
oh... that is new to me!. I just quick search google, the only procedure I found was to disconnect battery for 15 mins to reset or clear with scanner... am I corected? or is there any other procedure??
no-no, not with scanner this time. (I dont know how).
there's another procedure with key on/off press button to reset the display error message.
I know this procedure is extremely RETARDED... it should clear itself once everything is made ok,
yet it does not.
Has anyone ever seen a Warnier/Orr diagram or decision tree for how the system with the keyless go works, or how it was intended to work? I'd sure like to see that if available.
It makes absolutely no sense to me why Mercedes would create a system where the car appears to talk with the keyless go fob endlessly when there is no particular event happening with either the fob or the car itself. The car itself, parked, turned off, has no function that I know of that would require a check to the key fob. Certainly, the key fob itself would have no reason to attempt to interact with the car. So why the continuous conversations?? Is that what is really happening?
I just completed the Keyless Go module upgrade. I guest not too many people take on this upgrade, so there was not many information online. The job is more involved than I thought. Need to remove lots of marterial/parts to get to the module. The module's bracket has some bolts hiding up high, not very obvious to find. Once the module was out, the job was straight forward. After this upgrade, disconnected the battery, scanned and cleared the codes, the "replace battery" message was still on. I am waiting to replace the cr2032 battery... hopefully it will fix that one for all. Thank you CaliBenz for the contribution and posts. In the coming days, I will follow these posts and update all the parts.
update: change the keyfob to CR2032. So far the "change battery" message has disappeared. The cr2032 is way too thick, couldnt be fit properly. I had to use force to jam it into the battery tray. Next time when It need to be removed will be a major problem. Let see how long will this bigger battery last.
