These instructions apply to the Hyundai Bayon Mk1 (BC3) 2021-Present.
For other models, please choose your vehicle here.
When the remote on a Hyundai Bayon (BC3, 2021–present) only locks the car from a pace away, ignores the odd button press, or dies altogether, the culprit is almost always the little coin cell inside it. The Bayon shares its keys with the sister i20, and depending on trim you’ll be holding one of two remotes: a 3-button folding “flip” key on lower, turn-to-start models, or the smart (keyless) fob that pairs with the engine start button on higher trims. Both take the same battery but open in different ways, so this guide covers each — plus how to tell a flat cell from a real fault, and why cutting a brand-new key is the one job you can’t finish at home.
How to Tell the Fob Battery Is Dying
- Shrinking range. You find yourself standing right next to the Bayon — or holding the fob against the door handle — to make it lock or unlock. That fading range is the classic first warning.
- The button LED goes dark. The remote’s indicator light no longer blinks when you press lock or unlock. It’s a quick way to prove the fob, not the car, has the problem.
- A “Key battery low” message. On smart-key Bayons the instrument cluster flags a low key-battery warning once the cell weakens — a clear, early prompt to swap it.
- Hit-and-miss in the cold. A cell that’s nearly spent struggles most on a frosty morning, so intermittent response in cold weather usually means the battery is on its way out.
A coin cell in a Bayon remote typically lasts two to four years. A smart fob sits in constant standby listening for the car, so it tends to run down a little sooner than a plain flip key. If yours is a few years old and showing any of the signs above, fit a fresh cell before you suspect the receiver or immobiliser.
The Battery You Need
Both the folding flip remote and the smart fob use a single CR2032 — a 3-volt lithium coin cell, 20 mm across and the most common key battery there is. You’ll find it in any supermarket, hardware shop or phone-accessory stand. Buy a fresh, good-quality branded cell: cheap or old-stock coin cells sag under the short burst of current the transmitter draws and can give weak range even when they read as “new”. If in any doubt, match the code printed on the cell you take out.
Method 1 — Folding “Flip” Remote
- Fold the metal blade closed so the fob is easier to grip.
- Look at the back of the fob for a small retaining screw. If there is one, undo it with a fine cross-head (Phillips) screwdriver and lift off the battery cover. If you see no screw, the case simply clips together — find the seam that runs around the edge and prise it apart gently with a flat plastic tool or a small coin.
- Note which way the old cell sits before you touch it, then ease it out from under its retaining clip.
- Drop the fresh CR2032 in the same orientation as the one you removed, seated firmly against the contacts.
- Refit the cover — drive the screw back just snug (the housing is plastic, so don’t overtighten) or press the clips home — then test every button.
Method 2 — Smart (Keyless) Fob
- Release the emergency blade first. Slide the small catch on the fob and pull the mechanical key blade straight out of its housing.
- Insert a flat plastic tool — or the emergency blade itself — into the slot the blade leaves behind, and twist gently to split the two halves of the case. Work your way round the seam rather than forcing one corner.
- Lift out the old cell, again noting its orientation as it comes free.
- Fit the new CR2032 the same way round the old one sat, pressed fully under its clip.
- Line the two halves up, click them back together, and slide the emergency blade home until it latches.
⚠️ Get the polarity right. A coin cell fitted upside down makes poor contact and can quietly discharge, leaving the key unresponsive — so always copy the orientation of the cell you removed rather than guessing which face goes up.
Confirm It Worked
Step back a few metres and lock, then unlock, the Bayon. Full range should return the instant the fresh cell is in. On a smart-key car the “Key battery low” message clears once the system next reads a healthy fob — sometimes immediately, occasionally only after a short drive. If the remote still hesitates, reopen it and check the cell is seated flat and the right way up.
If a Fresh Cell Doesn’t Fix It
- Re-check seating and orientation. A cell that isn’t sitting flush under its clip, or that went in the wrong way round, is the most common reason a “new” battery changes nothing.
- 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 before you write the fob off.
- Warning slow to clear? The low-key alert can take a drive cycle or two to disappear. Rarely, a weak car 12 V battery mimics key faults — if the Bayon itself is sluggish to wake or the central locking behaves oddly, the vehicle battery is worth checking too.
- Still dead with a known-good cell? If the LED won’t light at all, the transmitter may have failed — but that’s uncommon next to a simple flat or upside-down battery.
New Key or Spare — Why It’s a Dealer Job
Changing the battery leaves the fob’s existing coding untouched, so nothing needs reprogramming afterwards. A new key is a different story: the Bayon’s immobiliser has to be accessed with a diagnostic tool to pair a fresh remote, and blank fobs (or emergency blades) are ordered and cut against the car’s VIN. That makes adding a spare or replacing a lost key a job for a Hyundai dealer or an auto-locksmith — so keep the battery in your spare fresh too, and you’re never down to a single working key.
Frequently Asked Questions
What battery does a Hyundai Bayon key fob take?
A single CR2032 3-volt lithium coin cell. It’s the same size whether you have the folding flip remote or the smart keyless fob.
Does the Bayon flip key use a different battery from the smart key?
No — both use the CR2032. The only real difference is how you open them: the flip key may have a small screw or simply clip together, while the smart fob opens once you slide out its emergency blade.
Which way up does the coin cell go?
Fit it exactly as the old one sat. Rather than memorise a “plus up” rule, look at the cell before you remove it and copy that orientation — a battery in the wrong way round can flatten itself and leave the key dead.
Do I need to reprogram the key after a battery change?
No. Swapping the cell doesn’t touch the fob’s coding, so it works straight away. Only a brand-new key needs pairing to the car.
How long should a Bayon key battery last?
Around two to four years. A smart fob left sitting near the car wakes constantly and tends to run down sooner than a flip remote you only press when you use it.
Can I still drive the Bayon if the fob battery is completely dead?
Yes. Use the mechanical blade inside the fob to unlock the driver’s door, and a keyless Bayon can still be started with a flat fob — hold the smart key against the start button as the car prompts. A dead cell won’t strand you.
If the remote stopped working suddenly right after the car battery was disconnected — rather than fading over weeks — the pairing, not the cell, is the likelier cause; a stored fault code can help pin it down, and you can look one up on autodtcs.com.
Independent guide — not affiliated with Hyundai. Always follow your official service manual and safety precautions. Read our full disclaimer.