Replace the Key Fob Battery

If the remote on your SEAT Leon Mk4 (KL, 2020–present) only locks the car when you are standing right next to it, or has stopped responding altogether, the cause is almost always the little coin cell inside the key — not the car. The Mk4 Leon, built on Volkswagen Group’s MQB Evo platform alongside the Mk8 Golf, Škoda Octavia and Cupra Formentor, uses the newer angular VAG remote. Depending on trim you either have the standard remote key (you press the buttons) or the KESSY keyless-entry fob (the car senses it in your pocket), but physically both are the same case, take the same battery and open the same way. Here is how to spot a dying cell, the exact battery you need, and the safe way to split this particular key open without cracking the plastic.

How to Tell the Fob Battery Is Dying

• Shrinking range. You have to be almost touching the car before it locks or unlocks — the classic first sign of a weak cell.
• The Leon shows a key-battery warning. The MQB Evo dashboard displays a “Key battery low” / replace-key-battery message in the driver information display when the fob voltage drops. On a KESSY car this often appears the moment you press the start button.
• Keyless entry gets unreliable. On a KESSY Leon the door handles stop sensing the key from a normal distance, so you find yourself pressing the buttons manually to get in.
• Cold-weather dropouts. A cell that is nearly flat sags further in the cold, so the key can work in a warm garage yet fail on a frosty morning.

A CR2032 in a Leon key normally lasts two to four years. A KESSY fob tends to run down a little sooner than a plain remote because it is constantly listening for the car, so if yours is a keyless model and it is a couple of years old, the cell is the first thing to change.

The Battery You Need

The Mk4 Leon key takes a single CR2032 3-volt lithium coin cell — the same widely sold cell used across the current VW, Škoda, Audi and Cupra keys. It is stocked in every supermarket, hardware shop and petrol station, so there is no need to buy a SEAT-branded one. Fit a good-quality branded cell (Panasonic, Varta, Duracell, Sony): cheap cells can sag under the brief high current the transmitter draws and give you short range even when they are “new”. If you ever see a CR2025 mentioned for older SEAT keys, that is a previous-generation key — the Mk4 KL uses the thicker CR2032.

How to Change the Battery

1. Release the emergency key blade. Slide or press the small catch on the side of the fob (near the key ring) and pull the metal emergency blade straight out. This blade is what unlocks the driver’s door if the fob is ever completely dead, so note how it sits.
2. Open the slot the blade left behind. With the blade removed, a narrow gap is exposed at that end of the case. Insert a small flat-blade screwdriver (or the emergency blade itself) into the seam and gently lever the two halves of the case apart. It runs on plastic clips, so a little twist along the seam pops it — there is no screw to undo on this key.
3. Lift out the old cell. Note which way up the CR2032 sits before you remove it. The positive (+) face is the larger flat side with the writing on it. Avoid touching the flat faces of the new cell with bare fingers — skin oils can foul the contacts over time.
4. Fit the new CR2032 the same way round. On this key the positive (+) side normally faces up towards the back cover, but always copy the orientation of the cell you took out rather than assuming — a Leon key fitted with the cell upside down simply will not work, even though the battery is brand new.
5. Click the case back together and press firmly around the edge until every clip snaps home, then slide the emergency blade back in until it latches.

⚠️ Get the polarity right. A CR2032 fitted the wrong way round will not power the transmitter and can slowly discharge against the contacts, so the single most useful thing you can do is memorise — or photograph — how the old cell sat before you lift it out.

Confirm It Worked

Stand back a few metres and lock, then unlock, the car with the buttons; full range should be back instantly. On a KESSY Leon, walk up and try the door handle to confirm keyless sensing has returned. The “Key battery low” message clears once the car has read a healthy fob — usually straight away, occasionally after one start-up cycle.

If a Fresh Cell Doesn’t Fix It

• Re-check the orientation and seating. An upside-down or loosely seated cell is by far the most common reason a “new” battery does nothing. Make sure it clicks firmly under its retaining clip.
• Wipe the contacts. A smear of finger grease or a trace of corrosion on the terminals is enough to cause dropouts — clean them with a dry cloth.
• Try the buttons manually. If keyless entry still lags but the lock/unlock buttons work at full range, the cell is fine and the KESSY handle sensors or aerials may be the issue rather than the key.
• Weak car battery. Rarely, a tired 12 V vehicle battery makes the car slow to wake and mimics key faults. If the Leon itself is sluggish to respond, look at the main battery before condemning 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 the instant you close the case. A new key is a different matter: the Mk4 Leon’s immobiliser is tied to the car’s component protection, and a blank fob has to be ordered against the VIN and coded to the car with diagnostic access — work only a SEAT dealer or a properly equipped auto-locksmith can do. That is why it pays to keep the battery in your spare key fresh too, so you are never down to a single working fob.

Frequently Asked Questions

What battery does a SEAT Leon Mk4 key take?

A single CR2032 3-volt lithium coin cell. It is the same battery for both the standard remote and the KESSY keyless fob on the KL-generation Leon.

Is the Leon key a CR2032 or a CR2025?

The Mk4 (2020-onward, KL) key uses the thicker CR2032. The CR2025 you may see quoted belongs to older SEAT keys — if in doubt, match the code printed on the cell you remove.

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

No. Swapping the cell does not affect the coding, so the fob is ready to use straight away. Only a brand-new key needs coding to the car.

How do I open the Leon key without breaking it?

Pull the emergency blade out first, then lever the case apart at the slot the blade leaves — it is held by plastic clips, not a screw, so work gently along the seam rather than forcing one spot.

How long should the key battery last?

Around two to four years. A KESSY keyless fob usually runs down a little sooner than a plain remote because it is always communicating with the car.

Can I still drive if the fob battery is completely dead?

Yes. Use the emergency blade inside the fob to unlock the driver’s door, then hold the fob against the marked spot on the steering column (or in the cup holder, per the on-screen prompt) and press the start button — the car reads the key by close-range signal even with a flat cell.

If the remote stopped working suddenly — right after the 12 V battery was disconnected, say, rather than fading over weeks — the fault is more likely a pairing or stored-code issue than the coin cell. You can look up what a logged fault code means on autodtcs.com.