Kia K900 key fob battery

Card or phone key

1. These years use a card-style key.
2. Passive cards draw power from the reader in the car, so there is nothing to swap.

Buy the exact size printed on the old cell (CR2412). The first two digits are the width in millimetres and the last two are the thickness in tenths of a millimetre.

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. Note which side of the old coin cell faces up (usually the side with the writing), lift it out with a plastic tool, and press the new one in the same way.
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.

Kia smart keys usually free the mechanical key with a button, and the case opens at the gap 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.