Mazda Mazda3 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. Turn it over: some older fobs use one small screw, newer ones just clip. Pry at the seam once any screw is out.
3. Replace the cell, keeping the + side where it was, and check the small metal tab still touches it.
4. Snap the case shut and watch for the lights to flash when you press lock at the car.

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. 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. 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. Snap the halves back together, slide the metal key home, and press each button, then try the start button from the driver's seat.

Mazda advanced keys usually have a knob or button that frees the auxiliary key; the cover lifts once the key is out.

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.

Flip key

1. Swing the key blade open first. On most flip keys the cell lives in the body behind the hinge.
2. Look along the edge for a notch. A coin turned in that notch usually separates the remote half from the blade half.
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 CR1620 is 16 mm across and 2.0 mm thick. It is easy to confuse with the 20 mm CR20xx sizes, which will not fit.