These instructions apply to the Toyota C-HR Mk2 (X2/XH2) 2023-Present.
For other models, please choose your vehicle here.
If the smart key for your Toyota C-HR Mk2 (2023–present) only unlocks the car when you’re standing right next to it, needs a second press to respond, or throws a low-key warning on the dash, the coin cell inside it has almost certainly run down. The second-generation C-HR ships with Toyota’s keyless Smart Key across the range — there is no cheaper flip-key variant — and, importantly, this newer fob does not use the CR2032 that older C-HRs and most earlier Toyotas took. It uses a larger cell. Here is how to spot a dying battery, the exact cell the Mk2 needs, the step-by-step swap, and why cutting a brand-new key is still a job for the dealer.
How to Tell the Fob Battery Is Dying
- Shrinking range. You have to be almost touching the car — or hold the fob against the door handle — before it locks or unlocks. This is the first and most reliable sign.
- A “key battery low” message. The C-HR Mk2 shows a low smart-key-battery warning in the driver’s multi-information display when the cell is weak. Don’t ignore it — range usually collapses within days of the first warning.
- You have to hold the fob to the start button. When the battery is nearly flat, keyless start can fail and the car tells you to touch the fob directly to the engine start switch to authenticate — a classic near-dead-cell symptom, not a fault. A marginal cell also drops out in cold weather, so a fob that works in a warm garage can go intermittent on a frosty morning.
A coin cell in a smart key that lives in your pocket all day typically lasts two to three years — a little less than a button-remote, because a keyless fob wakes and “talks” to the car whenever it’s near it. If yours is that age and doing any of the above, fit a fresh cell before suspecting the car.
The Battery You Need
The Toyota C-HR Mk2 smart key takes a single CR2450 3-volt lithium coin cell. This is the wider, higher-capacity cell Toyota moved to across its 2023-onward range (the same generation of key you’ll find on the current Prius, Corolla Cross, RAV4 and bZ4X). It is not interchangeable with the CR2032 used by the first-generation C-HR: the CR2450 is 24.5 mm across and thicker, so the smaller cell simply won’t seat or make contact. Buy a good-quality branded CR2450; cheap cells sag under the brief current spike the transmitter draws and can give poor range even when “new”.
How to Replace the Battery
- Release the emergency key. Slide the small latch on the top edge of the fob across and pull the mechanical emergency blade straight out of the body. Set it aside — you’ll use it as a lever.
- Open the case. With the blade removed, a slot is exposed where it sat. Insert the tip of the emergency blade (or a small flat-blade screwdriver wrapped in tape to avoid marks) into that slot and gently twist to pop the two halves apart. Work round the seam if needed — the halves are clipped, not screwed, so no fine cross-head driver is involved on this generation.
- Get to the cell. Open the fob and locate the CR2450 in its holder. On this newer Toyota key the circuit board may need to be eased up slightly to free the coin cell that sits beneath or beside it — lift gently and don’t force the board.
- Note the orientation, then swap. Before you remove the old cell, look at which face is visible (the marked, printed side is the positive terminal). Slide the flat cell out from under its retaining clip and fit the new CR2450 the same way round.
- Reassemble. Seat the circuit board back down, press the two halves of the case together until they click all the way round, then slide the mechanical emergency blade back in until its latch clicks home. Test every button.
⚠️ Match the polarity of the cell you removed. A coin cell fitted upside-down won’t power the fob and can slowly discharge against the contacts. The safest guide is always the orientation of the old cell — note it before it comes out, and copy it exactly.
Make Sure It Took
Stand back a few metres and lock, then unlock, the car. Full range should return straight away, and keyless entry should trigger from the door handle without you pressing anything. The “key battery low” message clears once the car next reads a healthy fob — sometimes after a short drive rather than the instant you close the case.
If a Fresh Cell Doesn’t Fix It
- Re-check the orientation and seating. An upside-down or loosely-seated cell is the single most common reason a “new” battery does nothing. Make sure it’s fully home under its clip against clean contacts.
- Confirm it’s genuinely a CR2450. It’s easy to grab a CR2032 out of habit — it will rattle in the holder and won’t make solid contact.
- Wipe the contacts. Finger grease or light corrosion on the terminals is enough to cause dropouts; clean them with a dry cloth before refitting.
- Try touching the fob to the start button. If the car still recognises the key when you hold the fob directly against the engine start switch, the immobiliser and coding are fine and the problem is purely the battery or its contact — not the car.
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 moment the case clicks shut. A replacement or additional key is a different matter: the C-HR Mk2’s immobiliser has to be paired to a blank fob with dealer-level diagnostic access, and blanks are ordered against the car’s VIN with proof of ownership. That makes adding a spare or replacing a lost key a job for a Toyota dealer or a qualified auto-locksmith — so it’s worth keeping the battery in your spare key fresh too, and never being down to a single working fob.
Frequently Asked Questions
What battery does a Toyota C-HR Mk2 key fob take?
A single CR2450 3-volt lithium coin cell. The second-generation (2023-onward) C-HR uses Toyota’s newer, larger key cell — not the CR2032 fitted to the first-generation car.
Can I use a CR2032 instead?
No. A CR2032 is physically smaller and thinner than the CR2450 the Mk2 needs, so it won’t seat properly or make reliable contact. Always fit the CR2450.
Do I have to reprogram the key after changing the battery?
No. Swapping the coin cell doesn’t affect the fob’s coding, so it’s ready to use immediately. Only a brand-new key needs pairing to the car.
Which way round does the battery go?
Fit the new CR2450 the same way up as the one you took out — note the orientation of the printed (positive) face before you remove the old cell, and match it. A cell put in upside-down won’t work and can discharge.
How long should the smart-key battery last?
Usually two to three years. A keyless fob wakes up whenever it’s near the car, so leaving it hanging by the door at home shortens its life — keep spare keys a little further from the vehicle.
Can I still drive if the fob battery is completely dead?
Yes. Use the mechanical emergency blade inside the fob to unlock the driver’s door, then hold the fob directly against the engine start switch and press it — the C-HR is designed to read the key this way even with a flat cell, so a dead battery won’t strand you.
If the remote stopped responding suddenly — for instance right after the 12 V battery was disconnected — rather than fading over weeks, the cause is more likely a pairing or stored fault than the coin cell. Look up any related code on autodtcs.com before assuming the key itself has failed.
Independent guide — not affiliated with Toyota. Always follow your official service manual and safety precautions. Read our full disclaimer.