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2014 E350
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Discussion Starter #1
Recently my 2014 E350 gave me a message, on the instrument cluster, to replace the battery in my key. OK, looked up the type of battery, bought one, inserted it, all done. I bought it at a local CVS where batteries don't sit for long, so I have faith the battery is good. Every time I start my MBZ it still gives me the message to replace the battery. This message remains, blocking out my MPH view, until I notice it and hit the OK button on the steering wheel.
I called my friendly Service Advisor, who suggested I get the key far away from the car where it couldn't be detected, then start the car with my spare key fob. He said this should reset my car. I did this with the spare and no message appeared. Very good. But, the next time I used my old key, there's the message again. The SA said if it remained, I have a bad key fob, maybe it got wet or dropped? No and No.
This isn't a big deal, I can continue to use my spare key, and this is the only hiccup my car has had in 21 months of ownership. But if anyone has a suggestion on how to reset the instruments to eliminate the message, I would appreciate your sharing. BTW, I have tried to eliminate it by bringing it up and hitting buttons, to no avail. Suggestions?
Thanks in advance.
 

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Recently my 2014 E350 gave me a message, on the instrument cluster, to replace the battery in my key. OK, looked up the type of battery, bought one, inserted it, all done. I bought it at a local CVS where batteries don't sit for long, so I have faith the battery is good. Every time I start my MBZ it still gives me the message to replace the battery. This message remains, blocking out my MPH view, until I notice it and hit the OK button on the steering wheel.

I called my friendly Service Advisor, who suggested I get the key far away from the car where it couldn't be detected, then start the car with my spare key fob. He said this should reset my car. I did this with the spare and no message appeared. Very good. But, the next time I used my old key, there's the message again. The SA said if it remained, I have a bad key fob, maybe it got wet or dropped? No and No.

This isn't a big deal, I can continue to use my spare key, and this is the only hiccup my car has had in 21 months of ownership. But if anyone has a suggestion on how to reset the instruments to eliminate the message, I would appreciate your sharing. BTW, I have tried to eliminate it by bringing it up and hitting buttons, to no avail. Suggestions?

Thanks in advance.


Try swapping the two batteries so to provoke the Spare Key to generate the message. If it does, then you know it?s the battery


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2014 E350
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Discussion Starter #3
Terrapin, I got both of my keys out and started swapping batteries and keys. I must admit that between the four parts, and running out to the car to test it, I am no longer sure of what I did to make it work. But I was able to make the message go away, and also come back several times. I now believe I am using the original key and the new battery, and the message is gone, so I am stopping while I’m ahead. Thanks for your input.

One thought- it may be that I did not let the key sit without a battery long enough (when I first put in a new battery) and the key held a charge long enough that the car did not recognize that it had a new battery. I don’t know if the key can do that, but I didn’t do anything but move batteries around between the keys and now it’s fine.
 

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Terrapin, I got both of my keys out and started swapping batteries and keys. I must admit that between the four parts, and running out to the car to test it, I am no longer sure of what I did to make it work. But I was able to make the message go away, and also come back several times. I now believe I am using the original key and the new battery, and the message is gone, so I am stopping while I’m ahead. Thanks for your input.



One thought- it may be that I did not let the key sit without a battery long enough (when I first put in a new battery) and the key held a charge long enough that the car did not recognize that it had a new battery. I don’t know if the key can do that, but I didn’t do anything but move batteries around between the keys and now it’s fine.


Sometimes a little luck helps too. Most important is that you resolved your problem and saved big bucks!

Congratulations,


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2011 S212, 1978 R107
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225 Posts
I bought some El Cheapo batteries from IKEA and went through two of them showing "replace Key battery" -- the third one fixed it. Perhaps there is a lot of variability in the batteries.
 

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2008 E350 4Matic, 2011 E350 4matic
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860 Posts
It would probably be helpful to just get a battery meter, they're cheap, under $10 and measure the voltage of the battery that you get. New they're 3.25-3.31 volts. I notice when I start getting the message that the voltage drops to about 3.06 but sometimes even at 3.11. If you have old/fake batteries I can see you getting that message all the time.
 

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2010 ML550
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Hello,

I have a similiar issue, but changing batteries in either key fob doesn't help, and the car is having trouble sensing either key. I have to repeatedly try to open or lock the door, and when it doesn't work I just have to manually press the key button to unlock/lock the doors. The car starts fine but the 'replace key battery' message never goes away.

It seems like the sensor in the car itself has gotten weak, and this weakening progressively got worse until the key would not work to unlock/lock the doors at all (again, works just fine every time when manually pressing the buttons). It was only after the smart function sensitivity had significantly faded over a 1-2wk period before the change key battery warning appeared.

Does anyone have any ideas of how to fix this issue?

Thanks in advance!
 

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2014 E350 station wagon gasoline
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275 Posts
I have exactly the same issue with my 2014 E350.
The message to change the battery in the key fob appeared about 6 months ago.
So I did, I bought a brand new battery but the message came up the next time I used the key even though I replaced the battery.

I have no problem unlocking the doors using the push button on the key fob or grabbing the door handle.
This tells me that the battery is strong enough to transmit the signal yet the message appears every time I start the car.

This morning however the message was "Key not detected" so I had to start the car using the actual key.
Then when I restarted the car after driving about an hour it detected the key and I could start the car with the push button, but the message to replace the battery appeared again.

I have a spare battery so I checked the voltage of the battery in the key fob and the spare one, both are at about 2.91-2.96V.

So I'd also like to know how to make the message disappear.

Thanks.
 

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2008 E350 4Matic, 2011 E350 4matic
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860 Posts
I have exactly the same issue with my 2014 E350.
The message to change the battery in the key fob appeared about 6 months ago.
So I did, I bought a brand new battery but the message came up the next time I used the key even though I replaced the battery.

I have no problem unlocking the doors using the push button on the key fob or grabbing the door handle.
This tells me that the battery is strong enough to transmit the signal yet the message appears every time I start the car.

This morning however the message was "Key not detected" so I had to start the car using the actual key.
Then when I restarted the car after driving about an hour it detected the key and I could start the car with the push button, but the message to replace the battery appeared again.

I have a spare battery so I checked the voltage of the battery in the key fob and the spare one, both are at about 2.91-2.96V.

So I'd also like to know how to make the message disappear.

Thanks.
Get some new batteries. New ones are at 3.25-3.35 volts. I get the message when the voltage drops down to 3.06. The ones you buy at the local store are usually sitting on the shelf too long. I've tried various brands on eBay, but lately the best ones seem to be Energizers which give me 3.35 volts, some of the Sony and Duracell only give me 3.25. I forget what brand MB uses but there's lots of fakes out there so hard to say which ones are really the best. I usually just get a 10 or 20 pack. (Two cars which use a total of 6 batteries).
 

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2014 E350 station wagon gasoline
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Get some new batteries. New ones are at 3.25-3.35 volts. I get the message when the voltage drops down to 3.06. The ones you buy at the local store are usually sitting on the shelf too long. I've tried various brands on eBay, but lately the best ones seem to be Energizers which give me 3.35 volts, some of the Sony and Duracell only give me 3.25. I forget what brand MB uses but there's lots of fakes out there so hard to say which ones are really the best. I usually just get a 10 or 20 pack. (Two cars which use a total of 6 batteries).
Thanks.
That might be the issue as when I checked the brand "new" battery I got from a convenience store the voltage was 2.96V.
However I use CR 2025 Panasonic battery and the voltage indicated on it is 3V.
Why would that be 3.35V when new?
And why would the car's computer consider 2.96V too low?
The message has been appearing for about 6 months and the battery voltage is almost the same now when I measured it 6 months ago.
Except for the message the key fob has been working just fine for the 6 months, so it is strange.
 

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2008 E350 4Matic, 2011 E350 4matic
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860 Posts
That's the nature of batteries. 9 volt batteries new aren't 9 volts, more like 9.5 or even 10 on lithium ones. Same with car batteries, fully charged is 12.7 volts. AA are more like 1.65.

I have keyless go so the batteries don't last long for me.
 

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Oddly, I’m having the exact same issue. Worse yet, after replacing the battery, I’m intermittently continuing to get the replace key battery warning. No discernible pattern as to when warning is on.

Will replace again just to see.


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w205
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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...
 

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w205
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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...
 

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W123 '83 200, W210 '98 E200K, W212 '13 E350
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I bought some El Cheapo batteries from IKEA and went through two of them showing "replace Key battery" -- the third one fixed it. Perhaps there is a lot of variability in the batteries.
Same here. Never had a problem with my dad's '98 W210 using cheap batteries, but on my '13 E350, a new Ikea battery wasn't good enough. Put in an Energizer Lithium ($5.99), and I haven't had any problems for a couple of weeks.
 

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2008 E350 4Matic, 2011 E350 4matic
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Same here. Never had a problem with my dad's '98 W210 using cheap batteries, but on my '13 E350, a new Ikea battery wasn't good enough. Put in an Energizer Lithium ($5.99), and I haven't had any problems for a couple of weeks.
They're all lithium. You can get a 10 pack of Energizers on eBay for about $4. They're the ones that are usually in the 3.30-3.35v range.

 

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3v is near the end of life on a Li battery CR2025 cell. The keylessgo fob is transmitting to turnnothr transmission off, push the lock bottom twice on the fob.
 
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