Hyundai Sonata key fob battery

Separate remote fob

1. A separate fob has no key blade inside, so it opens with nothing but a coin or a small screwdriver.
2. Look for a screw on the back or a notch on the edge. Remove the screw if present, then twist a coin in the notch to split the case.
3. Replace the cell, keeping the + side where it was, and check the small metal tab still touches it.
4. Close the fob and test it. If it does not work, open it again and check the cell is seated flat.

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. Use the slot where the metal key sat. Twist, do not lever hard, and work along the seam until the halves separate.
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. Snap the halves back together, slide the metal key home, and press each button, then try the start button from the driver's seat.

Hyundai smart keys usually have a button that releases the mechanical key; a flat tool in the gap then opens the case.

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.

A CR2450 is 24.5 mm across and 5.0 mm thick, much fatter than a CR2032. A thinner cell will rattle and lose contact, so buy the exact size.

Flip key

1. Swing the key blade open first. On most flip keys the cell lives in the body behind the hinge.
2. Some flip keys have a screw on the back; others just clip. Remove the screw if there is one, then pry gently at the seam.
3. Take out the old cell, noting which side faced you, and fit the new one the same way.
4. Close it up, check the blade still flips cleanly, and test the buttons at the car.

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.