ram0201

Does the charging happen inside the cup holder where there is a place to keep the key? or is it just a slot? Will the keyfob ever need batteries (or do they recharge like a phone battery?) if so, which way do we place it ?

superswiss

The key fob battery is not rechargeable. It's a CR2032 coin cell battery that you'll eventually need to replace. You should be getting a warning in the instrument cluster if the battery is low and needs replacing. They should last quite a while as the new key fobs in the W213 have a motion sensor in them, and they go to sleep if they don't sense any motion for 2 minutes. This is primarily for security to avoid the relay attacks where thieves use a device to relay the signal from your key fob sitting by your front door for example to the car in your driveway and steel it. By going to sleep the fob no longer sends out a signal until it sense motion again, and the added bonus is it preserves the battery. I'm going on three years now with my 2019 C63S with the original battery in the fob (same fob as the W213).

FYI...the place in the cup holder is to start the car if the fob battery is dead. It temporarily energizes the key fob

W205C43PFL

That ^

Another thing to note is if you take your vehicle to service at a dealership and purchased PPM (it includes swapping the key fob battery as part of the service). Although I heard that some dealerships don't do this or they don't do it in certain countries. In Canada, for example, the service includes a key fob battery change.

ua549

I replace the key fob battery at 18 months. Battery life depends on how much you use the key fob. I don't drive many miles, but make many 1-2 mile trips where I lock, close windows and unlock several times a day. Closing windows requires that the lock button be pressed until the windows are fully closed.

Elvisfan0108

Don’t you have keyless entry? The only thing I use the FOB for is the trunk. Since the Cab doesn’t have a button for the trunk on the outside.

superswiss

I was kinda wondering the same thing. One can place their finger on the square sensor on the door handle and don't let go until the windows are closed. No need to really take the fob out ever. Other than the cabs, most other models at least in the USA have handsfree access standard, so the trunk can be opened with a kick motion, which is what I do with my C63S coupe since there is also no button to open the trunk, but it has handsfree access.

JTK44

I have PPM. My dealer wanted $12 to replace the battery. I bought two on EBay for $1.69

Mikey53

Without a powered and functioning FOB, keyless entry doesn’t work. It’s being used whether you pull it out of your pocket or not.

W205C43PFL

I see so ya it does depend on countries. On my it says key fob battery with a part number N/C under PPM.

teksurv

A bit off topic but curious, the C coupe does not allow you to open the trunk manually? On my E coupe, you push the top of the Mercedes emblem (also where rear camera is) to manually open the trunk. I also have kick to open as an option.

superswiss

Nope, no manual opening the trunk. The emblem only pops open for the camera.

Elvisfan0108

I’m sure the power used isn’t the same. When the button is pushed , the FOB is transmitting a stronger signal. Try taping down one of the buttons and see how long the battery lasts.

superswiss

Correct, keyless entry is based on ultra-wideband, which is a low energy short-range radio technology, similar to Bluetooth LE in its goals to be very power efficient. Because it only has to work for a very short range, the power level is very low. Pressing a button on the fob sends a much more targeted signal and travels over a longer distance. You can lock/unlock the car from much farther away using the buttons on the fob, so that requires a higher powered signal. Keyless entry is deliberately only meant to work when you are standing right next to the door handle, so it's a very weak signal that uses very little power.

https://en.wikipedia.org/wiki/Ultra-wideband

W205C43PFL

Thanks for your explanation superswiss. Do you happen to know if keyless go constantly emit a signal when in your pocket or it only starts communicating when the car started searching and prompting for the signal to be broadcasted. Sort of like the car saying "Please wake up key, I need more information to confirm if I should authorize this access" or is it what I asked in the pervious sentence "Oh, good to see you door here is the identification, please confirm and grant access".
and...Which one do you prefer?

superswiss

I'm not intimately familiar with the specific protocol, but 99% sure the communication is initiated by the car and the fob responds. This is how digital locks I'm more familiar with work. They all use a beacon approach and if a key device comes within range of a recognized lock it responds to the beacon. These devices use proximity protocols. They basically first detect that they are in proximity of a locking device they recognize and then start the authentication handshake. NFC works the same. If you use touchless pay at a store for example, the reader initiates the communication and the NFC chip responds.

W205C43PFL

Yup, that sounds like the better approach and to conserve battery, thanks for your reply.

Elvisfan0108

I thought I’d go one step further. Since you can lock the car by touching almost anywhere on the door handle with your hand, I thought I would see if I can use the whole area to put the windows up. Apparently not. It’s the square sensor for that.

superswiss

Yep, only the square sensor works for the convenience closing, but otherwise you can touch anywhere on the outside part of the handle to just lock the car.