Key Fob Battery

Most keys use a coin cell such as CR2032 or CR2025. Batteries usually last a few years. Many cars show a warning when it is low. Keyless start often still works with a flat key battery because the car can read the transponder chip at close range through an emergency coil.

The battery powers the transmitter that sends the lock and unlock signals.

With a dead battery you can usually still start by holding the key near a marked spot. Replace with the correct type and observe polarity.