Lincoln MKS key fob battery

Key with remote in the head

1. Here the key blade and remote are one piece. You open the plastic head, not the blade.
2. Work a thin flat tool into the seam near the blade and twist; go round slowly if it does not open at once.
3. Replace the cell with the same face showing, and make sure the rubber keypad sits flat before closing.
4. Snap it closed and press each button. The car still starts with a dead remote battery on most of these keys, because the start chip needs no battery.

A CR2032 is 20 mm across and 3.2 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. Most push-button fobs hide a metal backup key. Press or slide its catch and draw the key out first.
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. 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.
4. Reassemble, refit the emergency key, and check that the car sees the fob when you press start.

Lincoln fobs usually have a release for the emergency key, and the case opens at the slot it leaves.

A CR2032 is 20 mm across and 3.2 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.