Replace Key Battery - warning
MBWorld Fanatic!
Joined: Feb 2014
Posts: 6,190
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From: MA
2008 E350 4Matic, 2011 E350 4matic
At 33 cents each on ebay I think the question is clearly answered, you get what you pay for and in this case $1.75 for a battery that you know is good sounds like a reasonable deal. If the $175 battery last for 18 months you won't need those 10 33 cent batteries, just my opinion.
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Joined: Jan 2009
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From: V E G A S
1922 Ford Model T / no OBD
I search the net and can't find solid answer if the key is on stand by mode when outside the car, or it shuts itself off. Did anyone actually try to see if keyless go would work with dead battery? I still "want" to believe the batteries are only for the remote buttons.
So far my keyless go car is garage queen, but 6 months after purchase battery still work.
Found interesting article on the net:
To unlock your car, firmly grip the driver door handle. To unlock all doors, grab any of the passenger handles. Most models have a removable push button located in the ignition and the dash that allows you to insert your Smartkey and use it as a regular car key.
If your button is in place, each press is like turning the key one position as long as you don’t press on the brake. With one touch you can turn on your vehicle’s accessories such as the radio.
Press the button a second time and the dash lights and all electrical items will turn on.
Press a third time with your foot off the brake, and everything turns off. You can also turn all features off by opening your door.
To turn the engine on, simply step on the brake and push the START/STOP button. To turn the engine off, stop the car, leave your foot on the brake, and press the START/STOP button once again. Remember to always shift to park and set the parking brake first.
If you want to lock your vehicles from the outside, simply touch the sensor located on the door handle. Forgot to close the windows and sunroof? No problem. Keep your finger on the sensor until the windows finish closing.
So far my keyless go car is garage queen, but 6 months after purchase battery still work.
Found interesting article on the net:
How to Use Mercedes-Benz KEYLESS GO®
With Mercedes-Benz KEYLESS GO®, you can unlock, lock, start and stop your car or even close your windows and sunroof from the OUTSIDE of your vehicle, simply by having your Smartkey in the immediate vicinity of your Mercedes-Benz.To unlock your car, firmly grip the driver door handle. To unlock all doors, grab any of the passenger handles. Most models have a removable push button located in the ignition and the dash that allows you to insert your Smartkey and use it as a regular car key.
If your button is in place, each press is like turning the key one position as long as you don’t press on the brake. With one touch you can turn on your vehicle’s accessories such as the radio.
Press the button a second time and the dash lights and all electrical items will turn on.
Press a third time with your foot off the brake, and everything turns off. You can also turn all features off by opening your door.
To turn the engine on, simply step on the brake and push the START/STOP button. To turn the engine off, stop the car, leave your foot on the brake, and press the START/STOP button once again. Remember to always shift to park and set the parking brake first.
If you want to lock your vehicles from the outside, simply touch the sensor located on the door handle. Forgot to close the windows and sunroof? No problem. Keep your finger on the sensor until the windows finish closing.
Last edited by kajtek1; Mar 2, 2019 at 03:34 PM.
MBWorld Fanatic!
Joined: Dec 2003
Posts: 1,283
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From: Central Coast, CA
2020 X7 xDrive40i, 2016 X3 sDrive28i
I just tested it. Removed battery from my key. Keyless go stops working completely. Cannot lock/unlock door or start car with push button. Car starts fine if you remove the button and insert key into the hole in the dash.
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Joined: Apr 2006
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From: Dallas-Ft.Worth,TX
2016 E350 Sport
Update... I had my car serviced for other reasons on Monday. While there, I asked my SA about this keyfob battery drainage issue. Both the SA and the Asst. Sve. Manager told me to store my key fob as far away from the car as possible after locking it.
"The car is on all the time," they said. "And if the car senses the key fob is within range, it will drain its battery faster." They added, "For sure, do NOT store your key fob in the car, or within the garage where it's parked."
Mercedes has offered Keyless Go in their cars for several years now. One would think the dealers have dealt with this question for the same amount of time and know what they are advising to customers. Believe what you want, though.
I keep my key fobs in my bedroom, one in a dresser drawer with all the other backup key fobs, and the other on top of the dresser. The dresser is probably 25+ yards from the car in a detached garage. The batteries in my key fobs are OEM to the car, built in July 2015... nearly 4-years ago.
Believe what you want, and do what you want, of course.
"The car is on all the time," they said. "And if the car senses the key fob is within range, it will drain its battery faster." They added, "For sure, do NOT store your key fob in the car, or within the garage where it's parked."
Mercedes has offered Keyless Go in their cars for several years now. One would think the dealers have dealt with this question for the same amount of time and know what they are advising to customers. Believe what you want, though.
I keep my key fobs in my bedroom, one in a dresser drawer with all the other backup key fobs, and the other on top of the dresser. The dresser is probably 25+ yards from the car in a detached garage. The batteries in my key fobs are OEM to the car, built in July 2015... nearly 4-years ago.
Believe what you want, and do what you want, of course.
Last edited by DFWdude; Apr 17, 2019 at 12:21 PM.
MBWorld Fanatic!
Joined: Jan 2009
Posts: 9,224
Likes: 1,798
From: V E G A S
1922 Ford Model T / no OBD
So the keyless go knob I got with the car is still alive after 6 months and I don't know how old battery was in it. We drive the car like 1-2 times a week, so that has to be a factor?
I am on the market for spare key. Anybody know better source than $380 (+ programming) at California dealer?
BTW the dispute about putting key far away from car reminds me several topics about Bluetooth in W211 section.
Similar if your family room sofa is close to the car, it is the car who is going to answer your cellphone.
I had my W211 park next to a camper I slept in and getting up in the morning I noticed Bluetooth puck in the car still active.
Good procedure on older cars was to observe cluster and interior lights to go off after 10 seconds from closing the door.
Now I need to ask DW to take keyless key (!) away and observe the lights.
I am on the market for spare key. Anybody know better source than $380 (+ programming) at California dealer?
BTW the dispute about putting key far away from car reminds me several topics about Bluetooth in W211 section.
Similar if your family room sofa is close to the car, it is the car who is going to answer your cellphone.
I had my W211 park next to a camper I slept in and getting up in the morning I noticed Bluetooth puck in the car still active.
Good procedure on older cars was to observe cluster and interior lights to go off after 10 seconds from closing the door.
Now I need to ask DW to take keyless key (!) away and observe the lights.
Last edited by kajtek1; Apr 17, 2019 at 12:58 PM.
MBWorld Fanatic!
Joined: Dec 2003
Posts: 1,283
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From: Central Coast, CA
2020 X7 xDrive40i, 2016 X3 sDrive28i
I did an experiment a couple years ago. Took my two key fobs, put in fresh batteries from same batch. Locked one in a safe in the bedroom about 50 ft away from the garage, put the other one in the key jar just inside the house about 15 feet from the car.
Both fobs gave me the low battery message about 6 months later. So as far as distance away from car, that doesn't seem to make any difference in terms of battery drain.
Both fobs gave me the low battery message about 6 months later. So as far as distance away from car, that doesn't seem to make any difference in terms of battery drain.
Out Of Control!!
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From: North Scottsdale, AZ
'71 Pinto
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Out Of Control!!
Joined: Jul 2003
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From: North Scottsdale, AZ
'71 Pinto
MBWorld Fanatic!
Joined: Apr 2006
Posts: 4,694
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From: Dallas-Ft.Worth,TX
2016 E350 Sport
Konigstiger, I forgot about the ability to de-activate key fobs. I have now done so with my backup fob in the dresser drawer. Thanks.
Something in return for you, "King Tiger".....
Something in return for you, "King Tiger".....
Senior Member
Joined: Jul 2013
Posts: 308
Likes: 76
2024 E350
You might be able to find lithium CR2025 batteries at Dollar Tree. They used to come as a 2-pack, which comes out to only 50 cents a battery, but they might be switching to single packs. The brand is Sunbeam. It's what I've used the past several years.
MBWorld Fanatic!
Joined: Apr 2006
Posts: 4,694
Likes: 1,829
From: Dallas-Ft.Worth,TX
2016 E350 Sport
You might be able to find lithium CR2025 batteries at Dollar Tree. They used to come as a 2-pack, which comes out to only 50 cents a battery, but they might be switching to single packs. The brand is Sunbeam. It's what I've used the past several years.
Today I stumbled across a 4-pack of Lithium CR2025s at Harbor Freight. I was more attracted by the "Lithium" label than the blue packaging they came in which reminded me of a brand name... only when I got them home did I realize they were "Thunderbolt" brand LOL!
Anyways, they test very strongly -- well above 3V -- so I will give them a go.
I suppose there should not be any problem using lithium batteries?
Last edited by DFWdude; Jun 19, 2019 at 05:09 PM.
Thanks.
Junior Member
Joined: Apr 2018
Posts: 62
Likes: 12
From: Louisiana
2013 E350 Bluetec Sport
key fob replacement
I'd suggest calling dealers in states that have no sales tax...and verify that they will ship to you(security readons). I paid $250ish in LA,
So the keyless go knob I got with the car is still alive after 6 months and I don't know how old battery was in it. We drive the car like 1-2 times a week, so that has to be a factor?
I am on the market for spare key. Anybody know better source than $380 (+ programming) at California dealer?
BTW the dispute about putting key far away from car reminds me several topics about Bluetooth in W211 section.
Similar if your family room sofa is close to the car, it is the car who is going to answer your cellphone.
I had my W211 park next to a camper I slept in and getting up in the morning I noticed Bluetooth puck in the car still active.
Good procedure on older cars was to observe cluster and interior lights to go off after 10 seconds from closing the door.
Now I need to ask DW to take keyless key (!) away and observe the lights.
I am on the market for spare key. Anybody know better source than $380 (+ programming) at California dealer?
BTW the dispute about putting key far away from car reminds me several topics about Bluetooth in W211 section.
Similar if your family room sofa is close to the car, it is the car who is going to answer your cellphone.
I had my W211 park next to a camper I slept in and getting up in the morning I noticed Bluetooth puck in the car still active.
Good procedure on older cars was to observe cluster and interior lights to go off after 10 seconds from closing the door.
Now I need to ask DW to take keyless key (!) away and observe the lights.
MBWorld Fanatic!
Joined: Jan 2009
Posts: 9,224
Likes: 1,798
From: V E G A S
1922 Ford Model T / no OBD
Is it $250 for keyless go?
About 7 years ago MB USA judged keys theft-prevention item and no longer allow shipping. Some dealers actually require car to be present before giving the key and for keyless go you need to program it anyway.
Since I posted the above, I was visiting California and went to dealer who sold me regural knob for $162 few years back. Now keyless key (how stupid is that?) with programming cost me about $500 but they include checking the tire pressure and resetting TPMS.
Obviously coffee and bananas
About 7 years ago MB USA judged keys theft-prevention item and no longer allow shipping. Some dealers actually require car to be present before giving the key and for keyless go you need to program it anyway.
Since I posted the above, I was visiting California and went to dealer who sold me regural knob for $162 few years back. Now keyless key (how stupid is that?) with programming cost me about $500 but they include checking the tire pressure and resetting TPMS.
Obviously coffee and bananas
Newbie
Joined: Jan 2015
Posts: 12
Likes: 3
From: Atlanta area
2014 E350, Polar White, sport package
Key battery
Yeah, but I got Energizer batteries before and they only lasted 4 months, same deal as the dealer Panasonic batteries. Never had mine last more than 6 months. Don't know if it's because I'm in the city and there's lots of other signals/cars around which make them work more than people who may live in a quieter suburb.
Newbie
Joined: Sep 2020
Posts: 2
Likes: 0
2015 C300
Key Battery Warning
I have a 2015 C300 W205, 2 key fobs, Keyless Go. This year started having very short battery life and then replacing the CR2025 battery would not clear the warning - keyless still worked.
Tried Energizer and Maxell batteries, both with 3.25 VDC before use, no luck
I tried bending the 4 small battery tabs up before insertion - no luck.
I tried the battery remove/replace in the car after starting had no success.
Then I tried the suggested replacement of the CR2025 with a CR2032 (20 mm diameter and 2.5 vs. 3.2 mm thick), tight fit but success on both keys!
What do I think the problem is? I would take the fob apart and try to perform a failure analysis, but a new, programed key from MB is $500+. From my background in PCBs and Failure Analysis, I think the small metal part that contacts the bottom of the battery also contacts the printed circuit board to make the battery connection to the circuit. These PCBs are inexpensive and the surface finishes are not very durable - over time the contact may be oxidized or worn and the extra thickness of the CR2032 battery increases the contact force that reduces the electrical resistance. This fix will increase the apparent voltage to the circuit and it will no longer think the battery is weak. The voltage difference between a good battery and a weak or dead battery is less than 0.5 volts, a poor contact can easily generate this type of voltage drop.
The upside is the 2032 battery will last longer, the downside is that it will be harder to remove when it has to be replaced.
Thanks for all the other posts on the internet that helped me find a fix for our car!
Tried Energizer and Maxell batteries, both with 3.25 VDC before use, no luck
I tried bending the 4 small battery tabs up before insertion - no luck.
I tried the battery remove/replace in the car after starting had no success.
Then I tried the suggested replacement of the CR2025 with a CR2032 (20 mm diameter and 2.5 vs. 3.2 mm thick), tight fit but success on both keys!
What do I think the problem is? I would take the fob apart and try to perform a failure analysis, but a new, programed key from MB is $500+. From my background in PCBs and Failure Analysis, I think the small metal part that contacts the bottom of the battery also contacts the printed circuit board to make the battery connection to the circuit. These PCBs are inexpensive and the surface finishes are not very durable - over time the contact may be oxidized or worn and the extra thickness of the CR2032 battery increases the contact force that reduces the electrical resistance. This fix will increase the apparent voltage to the circuit and it will no longer think the battery is weak. The voltage difference between a good battery and a weak or dead battery is less than 0.5 volts, a poor contact can easily generate this type of voltage drop.
The upside is the 2032 battery will last longer, the downside is that it will be harder to remove when it has to be replaced.
Thanks for all the other posts on the internet that helped me find a fix for our car!
MBWorld Fanatic!
Joined: Apr 2006
Posts: 4,694
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From: Dallas-Ft.Worth,TX
2016 E350 Sport
As noted in post #39, I replaced the battery in June, 2019, after more than 15+ months without issues. (That's 15 months after I acquired the car... I have no idea how many months before the battery lived in the car before I bought it.)
It's now been 15 months and counting on the replacement, and the fob battery is still going strong.
It's now been 15 months and counting on the replacement, and the fob battery is still going strong.
Super Member
Joined: Nov 2018
Posts: 510
Likes: 64
From: Dallas Texas USA
2023 AMG EQE 53
I've never had a problem but maybe a tiny dab of dielectric grease on the contact would prevent oxidation. Failing that there is conductive grease, s very tiny dab of that.
Newbie
Joined: Sep 2020
Posts: 2
Likes: 0
2015 C300
As noted in post #39, I replaced the battery in June, 2019, after more than 15+ months without issues. (That's 15 months after I acquired the car... I have no idea how many months before the battery lived in the car before I bought it.)
It's now been 15 months and counting on the replacement, and the fob battery is still going strong.
It's now been 15 months and counting on the replacement, and the fob battery is still going strong.
Super Member
Joined: Nov 2011
Posts: 973
Likes: 376
From: Austin, TX
2013 SL550 BiTurbo
CR2032 FTW!!! 
Replaced the 25's w/32's almost 2 years ago...no issues since for me.
Just curious, but did you replace the batteries in both keys, then use both keys to operate/unlock/start the car separately? My wife's key battery was low, but mine was not. Even though, when I used my key, I would get the "low key battery" warning in the dash. Changed my batteries and I still got the message. I had to change her batteries, get my key away from the car and use hers to open/start the car, then the warning went away.
Replaced the 25's w/32's almost 2 years ago...no issues since for me.
Just curious, but did you replace the batteries in both keys, then use both keys to operate/unlock/start the car separately? My wife's key battery was low, but mine was not. Even though, when I used my key, I would get the "low key battery" warning in the dash. Changed my batteries and I still got the message. I had to change her batteries, get my key away from the car and use hers to open/start the car, then the warning went away.
