nycebo

Happy to have read this thread because my new car (<1 month) wouldn't unlock a couple days ago. Almost panicked, thinking that something was wrong with the alarm or the car itself, but then remembered this thread and immediately suspected that I had a battery issue. Plopped in a new CR2025 and things worked perfectly. I'll now keep a spare in the car just in case (when) it happens again.

7benzandcountin

Mercedes Genuine are Eunice at least one of the brands they recommend. 2/5.95 from an outfit in Georgia. Eunice bulk =Amazon 50 pc 10.00 something. Is there a good , better, best - (longline battery) Philips guarantees 80% after 2 years in the device, on and on -- I would assume a German battery should be better?? Happy Memorial Day 2013 .

Jinggyjin

Do you have any problem removing it from the slot? I tried 2032 and that just stuck there like a rock..

Sunnyslope48

I know a lot of people think that having a key near the car causes some communication between the two. I do NOT think this is true. It doesn't make sense. What would be the point? What would they talk about? If you touch your door handles, put your foot under the trunk area, push the start button, push a button on the remote, then there is some communication, but not just while the car is sitting there 24hrs a day. There has to be some action at the car initiated by a person to initiate the conversation.

belarus27

i today changed mine in the morning , its been about a year- a year and a half.
but not because it was done , but cuz i got a random No key message in cluster , and since i was leaving to work, just to be safe , i decided to change it. Renata battarie , pretty good. cr 2025 i believe

dchar

With keyless systems, the car and key will be communicating with each other so that the car knows that the key is within proximity. This allows the owner to walk up, touch the door handle to unlock, and start the car with the button (when key is inside the car). Some cars will light up puddle lamps when you are very close.

Sunnyslope48

In my car, it is the touching of the handle that initiates the 'conversation' between the fob and the car, not that the car is 'broadcasting' to see if the key fob is near the car. As for starting the car, the touching of the start button initiates the conversation, then the determination is made to see if the key is inside the car. If the trunk opening sensor is activated by putting your foot under the car, then the conversation is initiated. I cannot think of a scenario where the car would send out a signal to communicate with the key fob to see if it will respond, unless it were initiated by some physical action at the car.

Why someone would design a system to be in constant contact with a device (key fob) that depends on very small batteries on the receiving end? The car has a HUGE SUPPLY of battery power (comparatively) to send out such signals, but what of the key fob with it's tiny battery?

My lights do not light up without some physical contact with the car or by contact with the key fob. Does yours? And under what conditions?

The reason I bring this up is not to be argumentative. I keep my key(s) within 6 feet of my car (other side of the garage wall) and my fob batteries have lasted almost a year for one of the fobs, and for over a year (car purchased 4/16, now 6/17) on the other, yet to be replaced. If the car were continuously communicating with the key fobs, certainly the batteries would have been depleted by now.

thenew3

Usually no, I just hold the key in one hand (with the battery opening facing down) and slap it against the other hand a couple of times and it'll pop out. The one time it didn't pop out, I took a very small flat head screw driver and just lightly pried on the edge of the battery and it came out.

cetialpha5

You could probably just use a small screwdriver or something to pop out the battery. I just happen to have an Xacto knife in my drawer so I always use that to pry it out. Mine have only been lasting about 4-8 months, but they're both keyless go fobs. Don't seem to have any luck with any magic brand of battery. The dealer installed one didn't last long either. I've tried Energizer, Sony, Duracell, Maxell, they all don't last long.

The G Man

I am getting about a 9 months to a year out of them. I think the key is to buy fresh batteries and not whatever is the cheapest on Ebay.

emr61

the problem is not the batteries...If you replace new battery that nearly 3,30volts its ok. But i established that every pressing the button, battery lost 0.01 volt... When the battery decrease to nearly 3,05 volts;

the massege appears in the car,
the red light on the key stops flashing
you can still open/close the doors or use the start button,
-BUT you can NOT close or open the windows using the key.(ex: press and hold the lock key to close all windows but you cant).

So we have to replace a new one in a quick period but its unacceptable because volt is still 3 and it should be 3...
I heard that this is a software fault and service has got a software to fix that situation. If someone has any experience about this software or something, please inform...

fmorelli

We have a 2014 GLK250 with GO. 2032 batteries get swapped every ~2 months. Been like that for the two years we've owned the car. Is this a software issue? It makes no sense. Today I checked the battery which is 3.051V, and of course the car is saying it needs to be replaced.

Filippo

kajtek1

We don't drive our Keyless Go car very much. It gets driven about twice a week. but it is coming close to a year since I bought it and I did not replace the batteries yet.
But my habit is, whenever I come home- key goes into the drawer about 40' from the car and I never use remote buttons.

DFWdude

I bought my W212 Keyless Go in March, 2018, and just replaced the battery in the primary fob. So, that's 18 months on one battery (at least... I don't know its use before I bought the car). I seldom use the buttons on the fob. BTW, my fobs use the CR2025 batteries (CR2032 will NOT fit in my fobs... cover will not close.)

Like Kajtek1, I store the fob a good 75 ft from the car on a walk-in closet shelf. The second fob is turned "off" and stored in a drawer below the primary.

I keep telling folks not to store the fob near the car, as it will consume the battery faster. Even my dealer tells me this. But some of you guys just don't listen.

cetialpha5

The key difference may be whether you have keyless go or not. Also I'm in the city and I have two cars so with 4 keys I'm not sure if they keyless go keys are talking to each other or maybe other cars passing by on the street. They are away from the car but don't know if other MB cars on the street wake the keys up. Mine basically last about 3-4 months before they drop below 3.05 and they start out at 3.30-3.25.

DFWdude

I believe I clearly stated mine is a Keyless Go car.

There is debate on whether the car talks to the key, or the key talks to the car, at what prompting, and at what range. I have chosen to eliminate any of the possibilities, by storing my fob with my wallet, house keys, comb and other pocket essentials... well out of range of the car. It's just a habit I developed decades ago that has found added benefit with this keyless go car.

Batteries are cheap, but my time to change them is not. Nor do I want to litter the landfills with dead CR2025 batteries more often than necessary.

BTW, I have two MBs as well, but the other one predates keyless go, and its key fob batteries easily last 5-6 years.

Managing 4 MB key fobs (plus the wife's 2 for her car) is no problem at all. I treat all of them the same.

Tuxdude

The keyfob will either need to transmit all the time or receive signals all the time for keyless entry to work. Regardless of whether it's transmit or receive, it consumes power doing it. This is the reason that keyless entry keyfobs drain battery quickly. Most MB keyless entry keyfobs support a way to stop transmitting/receiving all the time and thereby allowing you to increase the battery life. In the recent keyfobs, double pressing the lock button when you lock the car will disable this auto transmit/receive and at the same time disable your keyless entry. You will need to press any button on your keyfob to start transmitting/receiving again.

It's also a security feature against relay attacks with Keyless entry systems. With the 2019 C63S keyfobs (and may be other MB models too with keyless entry), even if you didn't use the double-press approach described above I've noticed that after two (or so) mins of no movement of the keyfob it automatically stops transmitting/receiving. Try placing a cardboard box near the door with the keyfob on top of it, wait a few minutes to see if keyless entry still works after two mins of no activity.

fmorelli

it's great to hear the people have keys to seem to work with reasonable battery life. Clearly as I've stated that is not the case for us. My wife's Mercedes is actually parked in the driveway. There is a two and a half car garage between the driveway and the inside of the house, where she keeps her purse with the keys inside the purse. There are three walls between the key and the car and I would say at least 30-40 feet of space on the conservative side. Still too close?

Filippo

KEY08

Probably, but move the key and see if it helps. The dealer replaces my Fob battery annually when the car goes in for it's A-B service. I never replace the batteries in between. My keys are stored well away from my car at all times and I lock the car in the garage as well. I never leave the car unlocked. If you leave the car unlocked it will come to life like some kind of bizarre toy story. With Airmatic it will start making self-level noises, and if you have full LED lighting the cooling fans will continue to come on and off as well. Best to just shut all of that down by locking the car and forcing it to sleep.

Arrie

I keep my key about 30 ft away from car behind one wall and one closet door. I replace my battery about every 6 months. I use 2032 battery.

kajtek1

I did the test. 2+ hr and the door still open/close with handle touch, so the key is active.
I never had desire to be good in electronics, but life forced me to learn how to operate numerous gadgets and my first guess would be that key has passive chip, read by car field.
But than why the door will not open when we remove batteries?
Technology surprised me thousands times in my live, so is it possible that the key emits constant signal who takes so little power, that pill-sized battery last over a year?
Or maybe car presence keeps the key active?
Frankly I am getting to a point where I don't want to know
I never lock my car in garage btw.

Arrie

Obviously the key sends a signal or pings as this is what the car thieves take advantage of. They go close enough of the car FOB and read the signal and transmit it to the receiver next to the car that then emits the signal and the car doors can be opened. The same signal then is taken inside the car and it can be started and driven away.

Tuxdude

I have the 2019 C63S and it's at least the case with my keyfob. There is a motion sensor in the keyfob and it automatically stops transmitting once it detects that it is idle for 2 mins. It might not be the case with all 2019+ keyfobs. This is an added safety protection against relay attacks.

As Arrie pointed out, attackers take advantage of the fact that the key is always transmitting, record the signal that the key transmitted and then replay it near the car to open the car and even start the car. Automatically stopping this transmission after some time prevents leveraging this attack if your keyfob is still without moving. If you're really worried, you should lock the car by pressing the lock button on the keyfob twice which disables transmitting to the car until you push any button on the keyfob again. This also increases the battery life.

masads

For those of us who have "older" keys that continuously "pings" and leaves the keys in close proximity, probably best to store one's keys in a tin can or the like to stop the 'pinging' from getting out.

It works for me as when I have my keys in a tin can and I try to open the car with the keys in there, my w212 does not unlock/lock. I am not sure if this is a long term remedy but it works and thus its a very basic DIY. Unless there are other suggestions...

kajtek1

You might want to check if you don't have metalized plastic bag from electronics.
Years ago, having toll transporder, I was given such a bag for putting transponder in, so it would not be detected when I am on carpool lanes.