Replace the Key Fob Battery

If the key for your Toyota Yaris Cross (2021–present) only locks the car from arm’s length, needs a second press to respond, or has stopped working altogether, the coin cell inside it is almost certainly flat. This first-generation Yaris Cross is sold with two very different keys depending on trim: a smart (keyless entry & start) fob that lets you unlock and start the car with the key still in your pocket, and a simpler bladed wireless remote on entry-level cars that you physically slot in to start. They do not take the same battery — and that catches a lot of owners out — so the first job is to work out which key you’re holding. Below is the exact cell for each, how to tell a dying battery from a real fault, and why cutting or coding a brand-new key is the one part of this you can’t finish on the driveway.

How to Tell the Fob Battery Is Dying

• Shrinking range. You have to be right next to the car — or almost touch the fob to the door handle — before it responds. This is the classic first warning on both key types.
• The remote’s LED stops flashing. On the bladed wireless remote the little indicator light no longer blinks when you press a button once the cell is weak, which quickly confirms it’s the key and not the car.
• A dash message. On smart-entry Yaris Cross models the multi-information display shows a low key battery warning when the fob’s cell is running down.
• Push-button start hesitates. If keyless start no longer recognises the fob first time, the car will still let you start by touching the fob directly to the START switch — a strong sign the battery, not the immobiliser, is the problem.
• Cold-morning dropouts. A cell that’s fine in mild weather but flaky on frosty mornings is nearly always on its way out.

A coin cell in a Yaris Cross key typically lasts two to four years. If yours is around that age and doing any of the above, fit a fresh battery before you start suspecting the car’s receiver or immobiliser.

The Battery You Need

This is where the Yaris Cross differs from many older Toyotas, so check which key you have before buying:

• Smart keyless fob (keyless entry, push-button start) — takes one CR2450 3-volt lithium coin cell. This is the larger 24.5 mm cell fitted to Toyota’s current smart keys; a CR2032 will physically fit the holder loosely but is the wrong part and won’t seat reliably.
• Bladed wireless remote (no keyless entry, key slots in to start) — takes one CR2032 3-volt lithium coin cell, the common supermarket size.

Buy a good-quality branded cell either way — cheap coin cells sag under the brief high current the transmitter draws and can give short range even when box-fresh. If you’re ever unsure, the safest rule is to match the code printed on the cell you take out.

Method 1 — Smart (Keyless) Fob — CR2450

1. Release the mechanical key. Slide the catch on the side of the fob and pull the emergency metal blade straight out. You’ll need the gap it leaves behind to open the case.
2. Split the case. Insert a flat plastic tool (or the emergency blade itself) into the seam the blade left and gently twist to separate the two halves. Work around the join rather than forcing one spot.
3. Lift out the old cell, noting which way it faces. Fit the new CR2450 with the positive (+) side facing up, exactly as Toyota specifies. Avoid touching the flat faces of the new cell with bare fingers.
4. Clip the halves back together until they seat all the way round, then slide the mechanical key back in until it latches.

Method 2 — Bladed Wireless Remote — CR2032

1. Prise off the key cover. With the integrated blade folded away, wrap the tip of a small flat-blade screwdriver in cloth and gently lever the cover off at the seam. The cloth protects the plastic from scratches and gouges.
2. Remove the battery cover underneath if your remote has a separate inner lid.
3. Swap the cell. Take out the old battery and fit the new CR2032 with the positive (+) side facing up. Make sure it sits flat and firmly under its clip.
4. Refit the covers, pressing until the seam closes flush, and test every button.

⚠️ Get the orientation right. Both Yaris Cross keys take the cell positive-side up, but always copy the way the old one sat before you removed it — a coin cell forced in upside down makes poor contact and can quietly drain, leaving you with a “dead” key that’s really just wrongly fitted.

Confirm It Worked

Stand back a few metres and lock, then unlock, the car. Full range should return straight away. On a keyless model, the low key battery message clears once the car next reads a healthy fob — that can take a drive cycle or two rather than clearing on the spot. If keyless start had been hesitating, it should now recognise the fob first time without you having to touch it to the START switch.

If a Fresh Cell Doesn’t Fix It

• Confirm you fitted the right size. The single most common Yaris Cross mistake is dropping a CR2032 into a smart fob that wants a CR2450 — it rattles, makes intermittent contact, and mimics a flat battery. Double-check the code.
• Re-check polarity and seating. The cell must sit positive-side up and clip down firmly against clean contacts.
• Wipe the contacts. A little finger grease or light corrosion on the terminals is enough to cause dropouts; clean them with a dry cloth.
• Warning still showing? Some low-key alerts only clear after the fob has been read a couple of times. If the car itself is also slow to wake or the central locking is erratic, a weak 12 V vehicle battery can imitate key faults — worth checking before you blame the fob.

New Key or Spare — Why It’s a Dealer Job

Changing the coin cell keeps the fob’s existing coding, so nothing needs reprogramming and the key works immediately. A new key is a different story: the mechanical blade has to be cut to the car’s key code, and a blank smart fob must be electronically paired to the Yaris Cross’s immobiliser with Toyota diagnostic equipment before it will start the car. Blank fobs are also ordered against the vehicle’s VIN. That makes adding a spare or replacing a lost key a job for a Toyota retailer or a qualified auto-locksmith — so keep the battery in your spare key fresh too, and you’ll never be down to a single working key.

Frequently Asked Questions

What battery does a Toyota Yaris Cross key take?

It depends on the key. The smart keyless fob uses a CR2450 3-volt lithium cell; the simpler bladed wireless remote on entry trims uses a CR2032. Check the code on the old cell if you’re not sure which you have.

Is the Yaris Cross smart key really CR2450 and not CR2032?

Yes. Toyota’s current smart entry & start fobs, including the Yaris Cross, use the larger CR2450. A CR2032 is the correct cell only for the non-keyless bladed remote, so it’s worth confirming before you buy.

Which way up does the battery go?

Positive (+) side up in both key types. Even so, note the orientation of the cell you remove and copy it — a battery fitted the wrong way makes poor contact and can flatten itself.

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

No. A battery swap doesn’t affect the fob’s coding, so it works straight away. Only a brand-new key needs cutting and programming.

How long should a Yaris Cross key battery last?

Usually two to four years. Frequent remote use, or leaving a keyless fob sitting near the car so it wakes constantly, will shorten that.

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

Yes. Use the mechanical blade inside the fob to unlock the driver’s door, then hold the smart fob directly against the engine START switch to start — the keyless system is designed to read the key by close contact even with a flat cell, so a dead battery won’t strand you.

If your remote died suddenly rather than fading — especially right after the car’s 12 V battery was disconnected — the cause is more likely a pairing or stored-fault issue than the coin cell. You can look up what a related warning or code means over on autodtcs.com.