Replace the Key Fob Battery

If the remote on your Fiat 500 (type 312, 2007–present) has started working only from a step away, needs a second or third press to lock the car, or has stopped flashing its little indicator light altogether, the coin cell inside the key is almost certainly flat. Nearly every 500 — from the early 2007–2015 cars through the 2015 facelift and on to the later Hybrid versions — carries the same folding “switchblade” flip key with a metal blade that swings out of the fob body, and Fiat did something slightly unusual with it: the battery screw is hidden behind that blade. Get the sequence right and it’s a two-minute job with a single small screwdriver. Here is how to tell a dying cell from a genuine fault, the exact battery you need, and why a brand-new key is the one part of this you can’t finish yourself.

How to Tell the Fob Battery Is Dying

• Shrinking range. You have to stand right beside the car — sometimes almost touch the fob to the door — before it will lock or unlock. This is the classic first warning and usually the only one you get.
• The indicator LED fades or stops. The 500’s flip key has a small light that blinks when you press a button. When it grows dim or fails to light at all on a press, the cell is nearly gone — a quick way to prove it’s the key and not the car.
• Two or three presses needed. A near-flat cell can manage one weak transmission but struggles to repeat, so the car responds intermittently.
• Worse in the cold. Lithium coin cells lose voltage in low temperatures, so a tired battery that just about works in summer can drop out completely on a frosty morning.

A CR2032 in a Fiat 500 key typically lasts two to four years. If yours is around that age and doing any of the above, fit a fresh cell before you start suspecting the receiver or the immobiliser.

The Battery You Need

The Fiat 500 flip key uses a single CR2032 — a 3-volt lithium coin cell, the most common fob battery there is and sold in any supermarket, hardware shop or petrol station. This is the size Fiat lists in the 500’s own owner handbook, and it is the same across the whole 312 run regardless of trim or model year. Buy a good branded cell rather than the cheapest multipack; low-quality cells sag under the brief high current the transmitter draws and can give short range even straight out of the packet.

How to Change the Fiat 500 Flip-Key Battery

1. Release the emergency blade first. Press the small catch on the side of the fob and let the metal key blade swing out. On the 500 this isn’t just for holding — swinging the blade clear is what uncovers the battery screw underneath it.
2. Undo the screw on the side of the fob. With the blade out you’ll see a small screw on the flank of the case. Turn it with a fine cross-head or small flat screwdriver — it usually only needs loosening, not fully removing, to free the battery carrier.
3. Slide out the battery holder. The little plastic tray that carries the cell pulls out of the fob body. If it’s stiff, ease it with a fingernail or a plastic tool rather than levering hard against the electronics.
4. Note the orientation, then swap the cell. Look at which face of the old CR2032 is showing before you lift it out, and fit the new one exactly the same way round. The 500’s handbook simply tells you to observe the battery’s polarity, so copy what you removed rather than guessing.
5. Refit and lock. Slide the holder back into the fob, turn the screw to lock it home — snug, not overtightened, the case is plastic — and fold the blade away. Test every button.

⚠️ Handle the cell by its edge and match the polarity. Skin grease on the flat faces can weaken the contact, and a cell fitted the wrong way round simply won’t power the transmitter — so keep the same side facing up as the one you took out.

Make Sure It Took

Fold the blade back into the fob, stand a few metres from the car and lock, then unlock. Full range should return the moment the fresh cell is seated, and the indicator LED should blink brightly again on each press. If the blade doesn’t click fully closed, the case halves aren’t quite home — open it and reseat the holder.

If a Fresh Cell Doesn’t Fix It

• Re-check the orientation and seating. A cell fitted upside down, or one not sitting flat in its tray, is the most common reason a “new” battery changes nothing.
• Clean the contacts. Wipe the battery tray’s metal terminals with a dry cloth; a film of grease or light corrosion is enough to cause dropouts.
• Confirm the cell is actually good. Coin cells can sit dead in a drawer for years — try a second known-fresh one 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 after a battery swap — the key works the instant the new cell is in. A brand-new or replacement key is a different matter: the blade has to be cut to the car, and the transponder and remote have to be matched to the 500’s immobiliser with dealer-level diagnostic equipment, ordered against the car’s VIN. That makes adding a spare or replacing a lost key a job for a Fiat dealer or an auto-locksmith. The practical takeaway: keep the battery in your spare key fresh too, so you’re never down to a single working remote.

Frequently Asked Questions

What battery does a Fiat 500 key fob take?

A single CR2032 3-volt lithium coin cell. It’s the size listed in the 500’s owner handbook and it’s the same across the whole 2007–present run, including the 2015 facelift and the later Hybrid.

How do I open the Fiat 500 key?

Press the catch and swing the metal emergency blade out — that uncovers a small screw on the side of the fob. Loosen the screw, slide out the battery holder, swap the cell, then refit the holder and retighten the screw.

Which way round does the battery go?

Fit the new CR2032 the same way up as the one you removed. Fiat’s handbook only says to observe polarity, so the safest guide is to note the orientation of the old cell before it comes out.

Do I need to reprogram the key after changing the battery?

No. A battery change doesn’t affect the fob’s coding, so it works straight away. Only cutting and coding a genuinely new key requires programming at a dealer or locksmith.

How long should a Fiat 500 key battery last?

Usually two to four years. Frequent locking and unlocking, or a key that lives near the car, will shorten that; a spare that’s rarely used can last longer.

Can I still get into the 500 if the fob is completely dead?

Yes. Swing out the emergency blade built into the key and use it in the driver’s door lock to get in, then start the car as normal — a flat remote battery doesn’t stop the mechanical key or the immobiliser transponder from working.

If your 500’s remote died suddenly alongside other electrical oddities rather than simply fading over months, the trigger may be a stored fault rather than the coin cell — you can look up what a given code means on autodtcs.com before booking any diagnosis.