Replacing the Mazda
Miata NC AKE Key
I knew the key battery was going dead when the car could not find the key so I could start the car-
it would still lock/unlock the doors by remote but the no-go when trying to start.
Push the release and remove the key.
Start to separate the key case by inserting a screwdriver in the slots on either side of where the key was removed and then working your way around the case.
After separating the two pieces, you will notice a round cover in the center- remove this to access the battery.
Remove, replace, reassemble- CR2025 battery type, verify before purchasing.
Here is the Mazda TSB with service points: