Replace the Key Fob Battery

Last updated: June 5, 2026

If the remote on your Toyota Aygo Mk2 (B40, 2014–2021) has become weak — you have to stand close to lock or unlock, or it’s become unreliable — the fob’s coin cell needs replacing. Depending on whether your car has keyless entry & start, the Aygo key takes a CR1632 or a CR2016. This guide covers both. It takes a couple of minutes with a small screwdriver.

Which Key Do You Have?

• With entry & start system (smart key): push-button start cars; has a pull-out emergency key. Takes a CR1632.
• Without entry & start system (standard remote): a fob that opens into upper and lower sections. Takes a CR2016.

Smart Key (CR1632)

1. Push and hold the release knob and pull the metal emergency key out of the fob.
2. Insert a screwdriver into the slot and gently remove the cover (don’t use excessive force).
3. Lift out the old CR1632 cell — avoid touching the terminals with your fingers.
4. Fit the new cell with the positive (+) side facing up.
5. Refit the cover and the emergency key, then check the remote works.

Standard Remote (CR2016)

1. Separate the upper section of the remote from the lower part.
2. Remove the button-cell casing and lift out the old CR2016 cell.
3. Fit the new cell with the positive (+) side facing up.
4. Refit the covers and check the remote locks and unlocks the car.

Does It Need Programming?

No — replacing the coin cell does not affect the fob’s pairing, so the key keeps working immediately. The Aygo does support owner re-registration of remotes via an ignition-cycling sequence, but that is an involved separate procedure; a brand-new key still needs the transponder programming, which a dealer or auto locksmith handles.

Frequently Asked Questions

What battery does the Aygo key take?

The keyless smart key uses a CR1632; the standard remote uses a CR2016. Check which type you have before buying.

Will the car still start if the smart-key battery dies?

Yes. Hold the fob against the start button (Toyota marks the spot) to start using the backup transponder. The emergency key in the fob unlocks the door.

Why shouldn’t I touch the battery terminals?

Skin oils leave a residue that increases contact resistance and shortens the new cell’s life. Handle it by the edge.

My remote still won’t work with a fresh cell — now what?

Re-open it and check the cell orientation and that the contacts are clean. If it’s still dead, the fob may have an internal fault and need replacing and programming by a dealer or locksmith.

To clear a service reminder after maintenance, see our Toyota Aygo service indicator reset guide. For warning lights, look up the code on autodtcs.com.