Which Battery Does My Car Key Fob Need?

Your car key fob has started playing up — you have to stand right next to the car and press the button three times, or the dashboard has flashed up a "key battery low" warning. The fix costs a couple of pounds and takes five minutes, but first you need to answer one question: which battery does your fob actually take?

Here's how to find out for certain, plus a quick guide to the batteries most car brands use.

Before you order anything, do this: open your fob and read the code on the old battery. Almost every key fob uses a lithium coin cell, and the type is engraved on the battery itself — CR2032, CR2025, CR1620 and so on.

That code isn't random. It tells you the battery's exact size:

• CR means it's a 3V lithium coin cell
• The first two digits are the diameter in millimetres
• The last two digits are the thickness in tenths of a millimetre

So a CR2032 is 20mm across and 3.2mm thick, while a CR2025 is the same diameter but slightly thinner. They are not interchangeable — a CR2025 will rattle loosely in a CR2032 slot and may lose contact, while a CR2032 may not physically fit where a CR2025 belongs.

If you can't open the fob easily, the battery type is also listed in your car's handbook (look under "remote control" or "key battery"), and it's usually moulded into the plastic inside the battery compartment.

The table below covers the batteries most commonly used by each manufacturer in the UK. Bear in mind that the exact type varies by model and year — brands often changed battery size between generations, and smart "keyless" fobs sometimes use a different cell from the older flip keys. Treat this as a starting point and always confirm against your old battery or handbook.

Spotted the pattern? CR2032 is far and away the most common key fob battery on UK roads. If you keep one spare battery in the kitchen drawer, make it that one — but check before you fit it.

Every fob is slightly different, but the process is broadly the same:

1. Release the emergency key blade if your fob has one — there's usually a sliding catch on the side or back. Removing the blade often reveals a slot for opening the case.
2. Split the fob casing. Most cases have a small notch designed for a coin or flat-blade screwdriver. Twist gently — don't force it, and work around the seam if it's stubborn. Some fobs (Toyota, Honda) have a small screw to remove first.
3. Note which way the battery sits. The flat side with the writing (positive, +) usually faces up, but not always — take a photo before you remove it.
4. Swap in the new battery, handling it by the edges. Grease from fingertips on the flat faces can reduce contact and shorten battery life.
5. Clip the case back together and test the buttons near the car.

A tip on quality: cheap unbranded coin cells often arrive half-discharged from long storage. A branded lithium cell costs pennies more and typically lasts three to five years in a fob — this is not the place to save 50p.

In almost all cases, no — the fob's code is stored in permanent memory, so a battery change won't affect the pairing with your car. Work reasonably quickly and don't press the buttons repeatedly while the battery is out.

A small number of older remotes can lose synchronisation. If your fob doesn't work after a battery change, check the battery is the right way up first, then look up the resync procedure for your model — it's often as simple as turning the ignition on and pressing a fob button. Your handbook will have the exact steps.

Don't wait for the fob to die completely. Replace the battery when you notice:

• Reduced range — you have to be closer to the car than you used to
• Multiple presses needed before the car responds
• A dashboard warning — most modern cars display "key battery low" or similar
• Keyless entry becoming unreliable — the door doesn't unlock when you grab the handle, but the buttons still work
• It's been more than three years — even a healthy-seeming battery is likely to fail in the depths of winter, when cold reduces its output and you least want to be locked out

You're not stranded. Nearly every fob contains a hidden mechanical key blade that slides or clips out — and even cars without a visible keyhole usually have one concealed under a cap on the driver's door handle. Keyless-start cars also have a backup method to start the engine with a dead fob, typically by holding the fob against a marked spot on the steering column or starting button. Your handbook covers both.

Lithium coin cells — especially the 20mm CR2032 — are seriously dangerous if swallowed. A swallowed coin cell can cause severe internal burns within two hours and requires immediate A&E attention. Store spares in their original blister packaging, keep old batteries out of reach until you dispose of them, and take dead cells to a battery recycling point (most supermarkets have one) rather than binning them.

To recap: pop your fob open, read the code on the old battery, and fit a fresh branded cell the same way round. For most drivers that means a CR2032, and both your fob and your spare in the drawer will thank you for buying a good one.

We stock the full range of key fob batteries — CR2032, CR2025, CR2016 and other coin cell sizes — from trusted brands like Energizer and GP Batteries. Browse our coin cell battery range with free UK delivery over £35.