Key FOB Battery Life
Super Member
Joined: Nov 2014
Posts: 577
Likes: 76
From: New York, NY
2021 Mercedes Benz e450 Wagon
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.
Newbie
Joined: May 2015
Posts: 9
Likes: 0
From: Tulsa, Oklahoma
C Class
Keyless Go -battery comment
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 .
Happy Memorial Day 2013 .
Member
Joined: May 2017
Posts: 95
Likes: 2
C63S
Actually CR2032 will fit the MB key. difference between 2025 and 2032 is one is 2.5mm thick while the other is 3.2mm thick.
2032 also has more power. Both are 3V, but 2025 is about 150mah while 2032 is about 200 to 225mah so close to a 50% increase in power.
It takes a little bit of pressure to push a 2032 into the battery compartment of the key but it does work. (tested it myself).
I'm actually using 2032's now in my key since I work in IT, do a lot of computer work and thus buy and use a lot of 2032 batteries.
2032 also has more power. Both are 3V, but 2025 is about 150mah while 2032 is about 200 to 225mah so close to a 50% increase in power.
It takes a little bit of pressure to push a 2032 into the battery compartment of the key but it does work. (tested it myself).
I'm actually using 2032's now in my key since I work in IT, do a lot of computer work and thus buy and use a lot of 2032 batteries.
Do you have any problem removing it from the slot? I tried 2032 and that just stuck there like a rock..
Senior Member
Joined: Apr 2016
Posts: 460
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From: Phoenix, AZ
2016 E350 Sport 2WD
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.
MBWorld Fanatic!
Joined: Jun 2013
Posts: 1,900
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From: Sacramento , CA
2010 e550 p2
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
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
Member
Joined: May 2017
Posts: 175
Likes: 24
From: SoCal
2020 Mercedes E450 Wagon
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.
Senior Member
Joined: Apr 2016
Posts: 460
Likes: 157
From: Phoenix, AZ
2016 E350 Sport 2WD
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.
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.
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From: Central Coast, CA
2020 X7 xDrive40i, 2016 X3 sDrive28i
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.
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MBWorld Fanatic!
Joined: Feb 2014
Posts: 6,190
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From: MA
2008 E350 4Matic, 2011 E350 4matic
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.
Newbie
Joined: Sep 2019
Posts: 2
Likes: 0
W205 - R129
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...
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...
Junior Member
Joined: Sep 2018
Posts: 17
Likes: 14
2013 GLK250
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
Filippo
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Joined: Jan 2009
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From: V E G A S
1922 Ford Model T / no OBD
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.
But my habit is, whenever I come home- key goes into the drawer about 40' from the car and I never use remote buttons.
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Joined: Apr 2006
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From: Dallas-Ft.Worth,TX
2016 E350 Sport
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.
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.
Last edited by DFWdude; Sep 29, 2019 at 05:51 PM.
MBWorld Fanatic!
Joined: Feb 2014
Posts: 6,190
Likes: 1,550
From: MA
2008 E350 4Matic, 2011 E350 4matic
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.
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.
MBWorld Fanatic!
Joined: Apr 2006
Posts: 4,695
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From: Dallas-Ft.Worth,TX
2016 E350 Sport
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.
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.
Last edited by DFWdude; Sep 29, 2019 at 08:38 PM.
Senior Member
Joined: Jan 2019
Posts: 439
Likes: 74
From: California
2019 AMG C63S
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.
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.
Junior Member
Joined: Sep 2018
Posts: 17
Likes: 14
2013 GLK250
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
Filippo
Banned
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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
Filippo
Last edited by RA72825; Sep 30, 2019 at 03:17 PM.
MBWorld Fanatic!
Joined: Oct 2010
Posts: 5,142
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From: Southern US
2010 E550, 273 Engine: 2012 S550, 278 Engine
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
Filippo
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Joined: Jan 2009
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From: V E G A S
1922 Ford Model T / no OBD
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.
Last edited by kajtek1; Sep 30, 2019 at 02:42 PM.
MBWorld Fanatic!
Joined: Oct 2010
Posts: 5,142
Likes: 1,293
From: Southern US
2010 E550, 273 Engine: 2012 S550, 278 Engine
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.
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.
Senior Member
Joined: Jan 2019
Posts: 439
Likes: 74
From: California
2019 AMG C63S
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.
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.
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.
Junior Member
Joined: Aug 2011
Posts: 36
Likes: 11
From: Toronto, Canada
2000 CLK320 (SOLD); 2016 E400 4MATIC
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...
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...
MBWorld Fanatic!
Joined: Jan 2009
Posts: 9,225
Likes: 1,798
From: V E G A S
1922 Ford Model T / no OBD
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.
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.
