These instructions apply to the Mazda 3 Mk3 (BM/BN) 2013-2018.
For other models, please choose your vehicle here.
If the remote or smart key on your Mazda 3 Mk3 (BM/BN, 2013–2018) only works from up close, or has stopped locking the car, the fob’s coin battery is almost always the cause — and it is a quick change. This guide shows how to swap the key fob battery and what needs a dealer.
First, Rule Out the Battery
A weak fob battery is the number-one reason a Mazda 3 remote becomes unreliable — short range, needing several presses, or hands-free entry/start failing. Most Mazda 3 keys use a CR2025 coin cell.
Replacing the Fob Battery
- Push and hold the release knob/catch and slide out the auxiliary (mechanical) key.
- Insert a small flat screwdriver into the gap and separate the two halves of the case.
- Pull out the button-cell cover and lift out the old CR2025 cell.
- Fit the new cell with the positive (+) side facing upwards.
- Check the O-ring seal is not distorted or displaced (it keeps the key water-resistant), then close the case and refit the auxiliary key.
- Test the remote.
After a battery change the key keeps its programming — no re-pairing needed.
Lost Key or Adding a Spare
The Mazda 3 requires a diagnostic tool (Mazda M-MDS) to program a key, and adding one generally needs at least two existing programmed keys present. A lost or extra key is best handled by a Mazda dealer or an auto-locksmith — there is no simple owner sequence. The home job is limited to renewing the battery in a key that already works. Up to six keys can be registered to the car.
If a Fresh Battery Doesn’t Fix It
- Check the cell type and polarity — a CR2025 fitted the wrong way gives no response.
- Use the auxiliary key to unlock the door, and hold the smart key against the start button to start if its battery is flat.
- Still nothing from any key? A receiver or body fault may be involved — check the code on autodtcs.com.
Frequently Asked Questions
What battery does the Mazda 3 key take?
Most use a CR2025 coin cell. Check the old one when you open the fob to confirm.
Do I need to reprogram after changing the battery?
No — programming is retained. Just fit the CR2025 the right way round, check the O-ring, and test.
Can I program a new Mazda 3 key myself?
No — the Mazda 3 needs the M-MDS tool (and usually two existing keys) to register a key, so a new or replacement key is best coded by a Mazda dealer or locksmith.
How do I start the car if the smart key is dead?
Use the auxiliary key to unlock, then hold the smart key against the start button and press — the car reads the transponder directly.
If the remote stopped working after a battery disconnection, see our Mazda 3 battery disconnect/reconnect guide.
Independent guide — not affiliated with Mazda. Always follow your official service manual and safety precautions. Read our full disclaimer.