Mercedes-Benz B-Class key fob battery
1 of the 4 model years listed for the Mercedes-Benz B-Class have a proven battery. The most common answer is CR2025. Rows below run oldest to newest; a year can appear twice when the car came with more than one kind of key.
- 2014Smart key
CR2025
Owner's manual: manualslib.com (checked Nov 1, 2026)
Manual text: “You will need a CR 2025 3 V cell battery.”
Find CR2025 on Amazon - 2015-2017Smart key
Not confirmed yet
Changing the battery
Smart key (push-button start)
- Start by freeing the hidden metal key: there is a latch or slide on the case, and the blade comes out once it moves.
- Look inside the empty key slot for a notch. Put the tip of the metal key or a small flat screwdriver wrapped in tape there and twist gently until the shell splits.
- Pop the old battery out with a toothpick or plastic pick, not a metal blade, and seat the new one with the + side matching the old one.
- Snap the halves back together, slide the metal key home, and press each button, then try the start button from the driver's seat.
On the common chrome Mercedes key, a slide at the back frees the mechanical key, and pushing that key into the opening releases the battery tray.
A CR2025 is 20 mm across and 2.5 mm thick. CR2032, CR2025 and CR2016 share the same width but not the same thickness, so a swap between them can leave a loose contact or a case that will not close.
Coin cells are a choking and burn hazard for children. Store the spares in their original pack, out of reach.