Question: Replace Key Battery - No Go
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Joined: May 2023
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ML250 BlueTech
Question: Replace Key Battery - No Go
Of all things that can go wrong in a Mercedes, this seems trivial, but...
On returning from a long trip, the dash display told me to Replace Key Battery. We have two fobs, so I replaced both batteries with the required CR2025. (My theory is that the buttons were pressed when stored in our luggage; it's kind of tight.)
Now, one fob works perfectly, but the other still causes the Replace message. I tried a second new battery, and the message persists. I pulled the contacts up a bit hoping to get a better connection, but no joy. The key works fine for starting and opening/locking doors, but for how long?
My concern is that it will work well, right up until the point that it doesn't.
Any hints?
On returning from a long trip, the dash display told me to Replace Key Battery. We have two fobs, so I replaced both batteries with the required CR2025. (My theory is that the buttons were pressed when stored in our luggage; it's kind of tight.)
Now, one fob works perfectly, but the other still causes the Replace message. I tried a second new battery, and the message persists. I pulled the contacts up a bit hoping to get a better connection, but no joy. The key works fine for starting and opening/locking doors, but for how long?
My concern is that it will work well, right up until the point that it doesn't.
Any hints?
MBWorld God!
Joined: Dec 2019
Posts: 33,224
Likes: 6,597
Of all things that can go wrong in a Mercedes, this seems trivial, but...
On returning from a long trip, the dash display told me to Replace Key Battery. We have two fobs, so I replaced both batteries with the required CR2025. (My theory is that the buttons were pressed when stored in our luggage; it's kind of tight.)
Now, one fob works perfectly, but the other still causes the Replace message. I tried a second new battery, and the message persists. I pulled the contacts up a bit hoping to get a better connection, but no joy. The key works fine for starting and opening/locking doors, but for how long?
My concern is that it will work well, right up until the point that it doesn't.
Any hints?
On returning from a long trip, the dash display told me to Replace Key Battery. We have two fobs, so I replaced both batteries with the required CR2025. (My theory is that the buttons were pressed when stored in our luggage; it's kind of tight.)
Now, one fob works perfectly, but the other still causes the Replace message. I tried a second new battery, and the message persists. I pulled the contacts up a bit hoping to get a better connection, but no joy. The key works fine for starting and opening/locking doors, but for how long?
My concern is that it will work well, right up until the point that it doesn't.
Any hints?
Thread Starter
Junior Member
Joined: May 2023
Posts: 55
Likes: 32
ML250 BlueTech
MBWorld God!
Joined: Dec 2019
Posts: 33,224
Likes: 6,597
Where did you buy the batteries? Asking because this might sound weird but new batteries can still be old, it might have be some bad old batteries in inventory that wasn't cleared out.
Thread Starter
Junior Member
Joined: May 2023
Posts: 55
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ML250 BlueTech
I could always try again, I suppose.
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From: Chicago
2015 ML350 4Matic, 2012 Jeep Wrangler
FOB battery
Of all things that can go wrong in a Mercedes, this seems trivial, but...
On returning from a long trip, the dash display told me to Replace Key Battery. We have two fobs, so I replaced both batteries with the required CR2025. (My theory is that the buttons were pressed when stored in our luggage; it's kind of tight.)
Now, one fob works perfectly, but the other still causes the Replace message. I tried a second new battery, and the message persists. I pulled the conta
cts up a bit hoping to get a better connection, but no joy. The key works fine for starting and opening/locking doors, but for how long?
My concern is that it will work well, right up until the point that it doesn't.
Any hints?
On returning from a long trip, the dash display told me to Replace Key Battery. We have two fobs, so I replaced both batteries with the required CR2025. (My theory is that the buttons were pressed when stored in our luggage; it's kind of tight.)
Now, one fob works perfectly, but the other still causes the Replace message. I tried a second new battery, and the message persists. I pulled the conta
cts up a bit hoping to get a better connection, but no joy. The key works fine for starting and opening/locking doors, but for how long?
My concern is that it will work well, right up until the point that it doesn't.
Any hints?
The 2025 is a 3v battery but has about 3.3 or more volts when new. I'd check voltage on your two batteries. Hope that helps.
Earl
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Member
Joined: Jan 2013
Posts: 190
Likes: 76
2013 ML550 US spec. Air+Offroad pkg
If you dont have one, you can get a cheap $10 multimeter at Harbor Freight, then touch the black lead to the flat/back of battery and red to the front to get your voltage. As said above, should read over 3v. If it does, then you are probably OK. Mine sometimes will do that for several days after battery replacement, but will go away with continued use (use it without other fob present for starting proximity lock/unlock, use the buttons too) until car relearns and resets to the fob with fresh battery. Ive had mine do that before and it just wouldnt reset to recognize the fresh battery. Hung up the FOB for a few months and used other one, then one day I tried the "low battery" FOB again and it worked just fine with no low battery message. Its a mystery.
Member
Joined: Jan 2013
Posts: 190
Likes: 76
2013 ML550 US spec. Air+Offroad pkg
Dont think replacing the battery is the problem...that is easy-peasy, the poster just cant get the car to recognize its a fresh battery.
Last edited by Leetom; Mar 13, 2025 at 09:14 PM.
