These instructions apply to the Abarth 124 Spider (2016-2020).
For other models, please choose your vehicle here.
The Abarth 124 Spider (2016–2020) shares far more than looks with the Mazda MX-5 — it is built on the same ND platform in Hiroshima, and that includes its key. The smart fob you carry is, underneath the Fiat/Abarth badging, a rebadged Mazda keyless key (the same Mitsubishi-made unit used on the ND MX-5), so it does not follow the usual Fiat pattern. That matters the moment you open it: the cell is not the CR2032 most Fiats use, and there is a small rubber seal inside that is easy to lose. If your 124 only locks from arm’s length, or the dash has started warning you about the key, here is exactly what to buy and how to fit it — the Mazda way, not the Fiat way.
How to Tell the Fob Battery Is Dying
- Shrinking range. You have to be right next to the car, or almost touching the door handle, before it will lock or unlock. This is usually the first sign.
- A flashing key warning after you switch off. On the 124 Spider the instrument-cluster key indicator light flashes (green) for around 30 seconds once the engine is switched off when the fob battery is getting low — the car’s way of telling you to change it before it dies completely.
- Passive entry gets unreliable. The keyless door handles and push-button start work intermittently, or only when the fob is held close to the START/STOP button.
- Cold-weather dropouts. A nearly flat cell struggles in the cold, so the fob may fail on a frosty morning and recover later.
A CR2025 in a 124 Spider fob typically lasts two to four years. Because both keys were usually supplied together, the spare in your drawer is the same age — if one is flat, plan to do both.
The Battery You Need
The Abarth 124 Spider smart key takes a single CR2025 — a 3-volt lithium coin cell, 20 mm across and 2.5 mm thick. This is the Mazda specification, and it is the one detail owners most often get wrong: the thicker CR2032 is not the correct cell here. A 2032 will physically start, and may even run for a while, but at 3.2 mm it spreads the contacts in the fob’s battery pouch, and afterwards a correct 2025 no longer seats reliably. Buy a good branded CR2025 and stick to it. One more Mazda-key quirk: some new cells ship with a bitter anti-swallow coating — wipe both faces clean with a dry cloth before fitting, or the fob may not read it.
How to Change the Battery
- Release the emergency key. Slide the small catch on the back of the fob and pull the mechanical blade straight out. You will use the empty slot it leaves to open the case.
- Split the case. Insert the tip of the emergency blade — or a small flat-blade screwdriver or a coin — into the seam exposed by the removed key and gently prise in the direction the arrows on the fob indicate. The back cover will pop free.
- Lift off the round battery cap. Under the cover is a small black plastic cap over the cell. Ease it off to reach the CR2025.
- Mind the rubber seal. There is a thin rubber ring that keeps moisture out. Do not scratch or lose it — if it lifts out, set it aside and refit it before you close the case.
- Swap the cell. Note how the old one sits, then remove it. Fit the new CR2025 with the positive (+) side facing up — the writing on the cell should be visible — and press it firmly into place.
- Reassemble. Refit the battery cap and the rubber ring, press the two case halves back together until they click all the way round, and slide the emergency blade home until it latches.
⚠️ Get the polarity right and keep the seal seated. The 124’s cell goes positive-side up; fitting it upside down means the fob simply won’t transmit, and a pinched or missing rubber ring lets damp into the electronics over time. Copy the orientation of the cell you removed and check the seal sits flat before you close it.
Did It Work?
Stand back a couple of metres and lock, then unlock, the car with the buttons — full range should return at once. Then test passive entry: with the fob in your pocket, grab a door handle, and press the START/STOP button to confirm keyless start reads the fob normally. Any low-key warning in the cluster should clear once the car has read a healthy fob, sometimes after the next drive rather than immediately.
If a Fresh Cell Doesn’t Fix It
- Re-check polarity and seating. Positive must face up, and the cell has to sit firmly under its contacts — a loose cell gives the same weak-range symptoms as a flat one.
- Confirm you fitted a CR2025. If a CR2032 was forced in previously, the pouch contacts may now be spread; a genuine 2025 can sit loose as a result.
- Clean the cell and contacts. Wipe any coating off a new battery and clean the terminals with a dry cloth — grease or the anti-swallow coating is a common cause of a “dead” new cell.
- Weak car battery? Rarely, a tired 12 V battery in the car itself can mimic key faults by leaving the receiver slow to wake — if the whole car feels sluggish to respond, look at the vehicle battery, not the fob.
New Key or Spare — Why It’s a Dealer Job
Changing the cell keeps the fob’s existing coding, so nothing needs reprogramming and the key works straight away. A new key is a different matter: because the 124 Spider uses the Mazda-based keyless system, a blank smart fob has to be ordered and coded to the car’s immobiliser with a diagnostic tool against the VIN. That makes adding a spare or replacing a lost key a job for a Fiat/Abarth dealer or an auto-locksmith — and cheap Mazda-lookalike fobs from online sellers often trigger a dashboard warning light because the part number doesn’t match. Keep the battery in your spare fresh, and you’ll never be down to a single working key.
Frequently Asked Questions
What battery does an Abarth 124 Spider key fob take?
A single CR2025 3-volt lithium coin cell. This is the Mazda specification — not the CR2032 used by most other Fiats — because the 124’s key is a rebadged Mazda MX-5 unit.
Can I use a CR2032 instead of a CR2025?
Avoid it. A CR2032 is thicker (3.2 mm versus 2.5 mm) and can permanently spread the contacts in the fob’s battery pouch, after which the correct CR2025 no longer seats reliably. Stick with the CR2025.
Which way up does the battery go?
Positive (+) side up, with the cell marking visible. Fitting it upside down stops the fob transmitting. Always match how the old cell was sitting.
Do I need to reprogram the key after changing the battery?
No. A battery swap doesn’t affect the coding, so the fob is ready to use immediately. Only a brand-new or replacement key needs coding to the car.
How long should a 124 Spider key battery last?
Typically two to four years. Leaving the fob sitting close to the car, where it wakes repeatedly, shortens that. Since both keys are usually the same age, replace the spare’s cell at the same time.
Can I still start the car if the fob battery is completely dead?
Yes. Use the emergency blade in the fob to unlock the driver’s door, then hold the fob against the START/STOP button — Fiat badge toward the button — and press it. The car reads the transponder at close range and starts normally, so a flat cell won’t strand you.
If your 124 Spider threw up a warning light or refused to start right after a fob or battery issue — rather than simply losing remote range — it may have logged a fault code worth reading before you assume the worst. You can look up what a stored code means on autodtcs.com.
Independent guide — not affiliated with Abarth. Always follow your official service manual and safety precautions. Read our full disclaimer.