These instructions apply to the Mazda CX-5 Mk2 (KF) 2017-2025.
For other models, please choose your vehicle here.
If the remote on your Mazda CX-5 Mk2 (KF, 2017–present) only locks the car when you’re standing right beside it, flashes its indicator weakly, or has stopped responding altogether, the cause is nearly always the little coin cell inside the fob. The second-generation CX-5 ships with Mazda’s smart (keyless / push-button start) key — the black rounded fob with a slide-out emergency blade — and unlike most rivals it does not take the near-universal CR2032. Get the cell right, work slowly at the seam, and this is a five-minute driveway job. Here is exactly what the KF uses, how to open it without cracking the case, and why a genuinely new key still means a trip to Mazda.
How to Tell the Fob Battery Is Dying
- You have to be almost touching the car. Range collapses first — the fob that used to work from across the car park now needs you within a metre or pressed against the door handle.
- Keyless entry gets fussy. The request switch on the door handle stops recognising the fob in your pocket, so you find yourself pressing the physical lock button instead of just grabbing the handle.
- A “Key Battery Low” message. The CX-5’s instrument cluster shows a low-key-battery warning (a key symbol with a warning) when the smart fob’s voltage drops — your earliest, clearest cue.
- Cold-morning dropouts. A cell that is fine at midday can sag below the threshold on a frosty morning; intermittent starts in the cold usually mean the battery is on its way out.
A coin cell in a CX-5 smart key typically lasts two to three years — a little less than average because the keyless system wakes the fob whenever it’s near the car. If yours is that old and doing any of the above, fit a fresh cell before you suspect the car.
The Battery You Need
The Mazda CX-5 smart key takes a CR2025 3-volt lithium coin cell — not the CR2032 that most other brands use. The two look almost identical, but the CR2025 is thinner (2.5 mm versus 3.2 mm). A CR2032 can be forced in and may even work briefly, but it strains the contacts and the case won’t close cleanly, so stick with the correct CR2025. Buy a good branded cell (Panasonic, Sony/Murata, Energizer, Duracell) — keyless systems are fussy about voltage, and a cheap cell can trip the low-battery warning while still reading as “new”.
How to Change the CX-5 Smart Key Battery
- Slide out the emergency blade first. On the back of the fob there’s a small sliding latch. Push it across and pull the metal auxiliary key straight out — this frees the case and gives you the gap you need to open it.
- Open the case at the blade slot. With the blade removed, look into the channel it left behind. Insert a flat plastic pry tool (or a small flat screwdriver wrapped in tape to avoid scratches) into that notch and gently twist to pop the two halves apart. Work around the seam rather than forcing one spot.
- Lift the two halves apart. The fob splits into a front and back shell. The CR2025 sits in a holder on the circuit board — don’t poke the board, just work at the battery.
- Note the orientation, then remove the old cell. Look at which face of the coin cell is visible before you lift it out. On most CX-5 keys the printed + face sits upward toward you as you open the fob — but the single golden rule is to copy whatever you removed.
- Fit the fresh CR2025. Slide it in the same way round as the old one, making sure it’s fully seated under its retaining clip. Handle it by the edges — finger grease on the flat faces can cause poor contact.
- Snap it back together and refit the blade. Line up the two shells and press until they click all the way round with no gap, then slide the emergency blade back in until it latches.
⚠️ Get the polarity right. A coin cell fitted the wrong way round won’t power the transmitter and, left in place, can slowly discharge against the contacts. If you didn’t note the orientation, the correct face is the one that matches the + and − markings moulded into the holder — never guess.
Confirm It Worked
Stand back a few metres and lock, then unlock, the car with the buttons. Full range should return at once. Then test keyless operation: with the fob in your pocket, touch the door handle to lock and unlock, and press the start button to confirm the car reads the key. The “Key Battery Low” message clears once the car next reads a healthy fob — sometimes after one drive cycle rather than the instant you close the fob.
If a Fresh Cell Doesn’t Fix It
- Re-check the cell type and seating. Confirm it really is a CR2025 (not a stray CR2032 or CR2016), and that it’s pressed fully under the clip against clean contacts.
- Wipe the contacts. A dry cloth or a cotton bud on the battery terminals removes the finger grease or light corrosion that causes dropouts.
- Try the backup start method. If the car won’t recognise the fob at all, hold the fob against the start button and press — the CX-5 can read the transponder at close range even with a weak or dead cell, which tells you the problem is the battery, not the car.
- Still nothing from the remote? A weak car 12 V battery can mimic key faults; if the CX-5 is generally slow to wake, have the vehicle battery checked before condemning the fob.
New Key or Spare — Why It’s a Dealer Job
Changing the coin cell leaves the fob’s existing coding untouched, so no reprogramming is needed — the key works the moment you close the case. A genuinely new key is a different matter: the CX-5’s smart-key system pairs each fob to the car’s immobiliser electronically, blank fobs have to be ordered against the VIN, and the emergency blade has to be cut to the car’s key code. That pairing needs Mazda diagnostic access, so adding a spare or replacing a lost key is a job for a Mazda dealer or an auto-locksmith. The cheap insurance is to keep your spare fob’s battery fresh too, so you’re never down to one working key.
Frequently Asked Questions
What battery does a Mazda CX-5 Mk2 key fob take?
A CR2025 3-volt lithium coin cell. It’s deliberately different from the CR2032 most other cars use — the CR2025 is the thinner of the two, so don’t substitute one for the other.
Can I use a CR2032 instead of a CR2025?
It’s not recommended. A CR2032 is 0.7 mm thicker; it may squeeze in and run for a while, but it stresses the contacts and can stop the case closing flush. Use the correct CR2025.
Which way round does the battery go?
Match the cell you took out — on most CX-5 keys the marked + face sits upward as you open the fob. Follow the +/− symbols moulded into the holder, and never fit it blind.
Do I need to reprogram the fob after a battery change?
No. The coding lives in the fob and isn’t affected by swapping the cell, so the smart key works straight away. Only a brand-new key needs pairing to the car.
How long should a CX-5 key battery last?
Usually two to three years. Because the keyless system wakes the fob whenever it’s near the car, leaving the key by the front door overnight shortens its life.
Can I still start the car if the fob battery is completely flat?
Yes. Use the emergency blade inside the fob to unlock the driver’s door, then hold the fob directly against the start button and press — the car reads the transponder at close range, so a dead cell won’t strand you.
If your CX-5’s remote died suddenly rather than fading — especially right after the 12 V battery was disconnected — the fault is more likely a pairing or electrical issue than the cell, and a stored code can point you to it. You can look up what any dashboard fault code means on autodtcs.com.
Independent guide — not affiliated with Mazda. Always follow your official service manual and safety precautions. Read our full disclaimer.