These instructions apply to the SEAT Arona Mk1 (KJ7) 2018-present.
For other models, please choose your vehicle here.
If the remote on your SEAT Arona (2018–present, MQB A0 platform) only locks the car from an arm’s length, drops out on cold mornings, or has stopped working altogether, the coin cell inside it has almost certainly gone flat. The Arona is sold with a switchblade “flip” remote as standard, and a keyless-entry smart fob (SEAT’s KESSY system) on higher trims and options packs. Both share the same battery and open the same VW-group way — slide out the emergency blade, then split the case at the seam — so the procedure below covers whichever key you have. Here is how to tell a dying cell from a real fault, the exact battery to buy, and why cutting a brand-new key is the one part you can’t do on the driveway.
How to Tell the Fob Battery Is Dying
- Shrinking range. You have to stand right next to the Arona — sometimes almost touching the door handle — before it locks or unlocks. This is the first and clearest sign.
- A dash warning. Keyless (KESSY) cars show a “Key battery low / replace key battery” message in the instrument cluster when the smart fob is weak. Don’t ignore it — it usually appears weeks before the fob quits.
- Keyless entry gets twitchy. The door handle sensors or push-button start respond only sometimes, or the car reports “key not found” even with the fob in your pocket.
- Cold-weather dropouts. A near-flat lithium cell loses voltage in the cold, so a fob that works at noon can fail first thing on a frosty morning.
A CR2032 in an Arona key typically lasts two to four years. A keyless fob tends to drain faster than a plain flip remote because it wakes up and “talks” to the car whenever it’s near it. If yours is a few years old and showing any of the above, fit a fresh cell before you suspect the receiver or immobiliser.
The Battery You Need
Both the flip remote and the KESSY smart fob take a single CR2032 3-volt lithium coin cell — the most common fob battery there is, sold in any supermarket, hardware shop or petrol station. A handful of very early Arona keys were built around the slightly thinner CR2025; the two look identical in diameter but the 2025 is thinner, so the safest rule is to match the code printed on the cell you take out. If it reads CR2032, buy CR2032; if CR2025, either replace like-for-like or use a CR2032 (it’s a touch thicker but seats fine in most holders). Buy a good branded cell — cheap ones sag under the brief current spike the transmitter draws and can give short range even when “new”.
How to Change the Battery — Flip Remote and KESSY Smart Fob
- Pop out the emergency blade. Press the small silver release button on the top edge of the fob; the metal key blade flips or slides straight out. On the smart KESSY fob the blade sits in the same place — pull it fully clear.
- Find the seam. With the blade removed you’ll see a narrow slot or gap in the case near the keyring end, where the two plastic halves meet.
- Split the case. Slide a coin (a £2 or €2 works well) or a flat plastic pry tool into the slot and twist gently to lever the two halves apart. Work slowly around the seam — there are small internal clips, and forcing it is how they snap. Avoid a metal screwdriver if you can; it marks the plastic.
- Note the orientation, then lift out the old cell. The CR2032 sits under a retaining clip. Photograph or memorise which way up it is before you disturb it.
- Fit the new cell. On the Arona the positive (+) side faces up — the same for both the flip and KESSY keys. Slide it under the clip with a fingertip; try not to bend the metal contacts, and keep your fingers off the flat faces so you don’t leave grease on the terminals.
- Close it up. Line up the two halves and press until they click all the way round, then push the emergency blade back in until it latches. Test every button and, on a keyless car, check the door handles and start button respond.
⚠️ Get the polarity right. Fitting the cell upside down won’t just leave the fob dead — a reversed cell can slowly discharge against the contacts, so a wrong-way battery may look flat within days. When in doubt, always copy the orientation of the cell you removed.
Did It Work?
Stand back a few metres and lock, then unlock, the car — full range should return at once. On a KESSY Arona the “key battery low” message clears the next time the car reads a healthy fob, which is sometimes instant and sometimes after one short drive rather than the moment you close the door.
If a Fresh Cell Doesn’t Fix It
- Re-check polarity and seating. A cell that isn’t fully home under its clip, or is in upside down, is the single most common reason a “new” battery seems dead.
- Clean the contacts. A smear of finger grease or light corrosion on the terminals is enough to cause dropouts — wipe them with a dry cloth.
- Re-sync the keyless fob. After a flat KESSY battery the car can lose the “handshake.” Hold the fob against the steering column (or the marked spot) and press the start button — this lets the car read the transponder directly and usually re-pairs it.
- Rule out the car’s own battery. A weak 12 V battery can mimic key faults, waking the car slowly or throwing “key not found.” If the Arona itself is sluggish to start, that’s worth checking before you blame the fob.
New Key or Spare — Why It’s a Dealer Job
Swapping the cell keeps the fob’s existing coding, so nothing needs reprogramming and the key works the instant you close the case. A brand-new key is a different matter: the Arona’s immobiliser is a secure VW-group component, so a fresh blade has to be cut to the car and the transponder coded to the immobiliser with diagnostic equipment. Blank KESSY fobs are ordered against the VIN. That makes adding a spare or replacing a lost key a job for a SEAT dealer or an auto-locksmith — so keep the battery in your spare key fresh too, and you’ll never be down to a single working fob.
Frequently Asked Questions
What battery does a SEAT Arona key fob take?
A single CR2032 3-volt lithium coin cell for both the flip remote and the KESSY keyless fob. A few very early keys used the thinner CR2025 — check the code stamped on the cell you remove and match it.
Which way up does the battery go?
Positive (+) side up on both Arona key types. Fit it the wrong way and the fob stays dead and the cell can quietly drain, so always match the orientation of the one you took out.
Do I need to reprogram the key after a battery change?
No. Changing the cell doesn’t affect the coding, so the fob works straight away. Only a brand-new key needs programming to the car. A keyless fob may just need a quick re-sync against the steering column if it lost contact while flat.
How do I open the Arona fob without breaking it?
Slide out the emergency blade first, then twist a coin or plastic tool in the slot it leaves to split the case at the seam. Go slowly around the join so you don’t snap the internal clips, and avoid a metal screwdriver, which marks the plastic.
How long should the key battery last?
Typically two to four years. A keyless KESSY fob drains faster than a plain flip key because it wakes whenever it’s near the car — leaving it sitting by the front door doesn’t help.
Can I still drive the Arona if the fob is completely dead?
Yes. Use the emergency blade hidden in the fob to unlock the driver’s door, then — on a keyless car — hold the fob flat against the steering column and press the start button; the car reads the transponder directly and starts even with a flat cell, so a dead battery won’t strand you.
If the remote stopped working suddenly — right after the 12 V battery was disconnected, say, rather than fading over weeks — the cause is more likely the pairing or a stored electrical fault than the cell. You can look up what any logged code means on autodtcs.com.
Independent guide — not affiliated with SEAT. Always follow your official service manual and safety precautions. Read our full disclaimer.