Mercedes-Benz Metris key fob battery

Remote key (form not stated in the source)

1. Key shape is not stated by the source. Compare your key with the types described on the how-it-works page.
2. Look for a notch, slide or screw on the case. A coin or small flat screwdriver, twisted gently, opens most fobs.
3. Swap the coin cell, keeping the same face showing, then make sure the doors respond.

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.

Smart key (push-button start)

1. Start by freeing the hidden metal key: there is a latch or slide on the case, and the blade comes out once it moves.
2. The gap left by the metal key usually has a pry point. A slow twist with a thin flat tool (tape on the tip saves the plastic) opens the two halves.
3. Before you take the old cell out, look at its face. Put the new cell in with the same side showing, and avoid touching both faces at once.
4. Close the case until it clicks all the way round, put the metal key back, then try the buttons and a push-button start.

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.