How to change your car key battery, make by make

What battery does my car key take?

Your owner's manual lists the battery code for your key. The manuals we read list a CR2032 for a 2020 to 2021 Toyota Corolla Hatch and a 2020 Mazda CX-5. Hyundai's online 2025 Tucson manual lists a CR2032 or a CR2450, depending on the key.

The code tells you the size. Energizer's datasheets give a CR2032 as up to 20 mm across and 3.2 mm thick. A CR2025 is the same width and 2.5 mm thick. A CR2016 is 1.6 mm thick. Same width, three different thicknesses.

Don't guess from the make alone. Hyundai's 2025 Tucson manual lists a CR2032 for the folding remote key and a CR2450 for the smart key. Mazda's 2019 European CX-5 manual lists a CR2025 for one key type and a CR2032 for the other. Two keys for the same model can take different cells. So look up your own key first.

Can I use a CR2032 instead of a CR2025?

Fit the code your manual lists. On Energizer's datasheets a CR2032 is 0.7 mm thicker than a CR2025. Mazda's CX-5 manual says to replace the key battery only with the same type. Toyota's Corolla manual is blunter: "If a wrong type of battery is used, it may explode."

How do I change a car key battery, step by step?

Take out the metal key if your fob has one. Fit a new coin cell of the same type, the same way up, then test the buttons at the car. The Toyota, Mazda and Hyundai manuals we read all open the cover, swap the cell and close it in that order. Toyota adds the test.

1. 1Step 1: Find the battery code in your owner's manual, and buy that exact type.
2. 2Step 2: Dry your hands. Toyota's manual says to always work with dry hands.
3. 3Step 3: Take out the metal key. On a Toyota Corolla smart key, step one is to release the lock and remove the mechanical key.
4. 4Step 4: Open the cover at its slot or gap. Toyota says to cover the tip of a flathead screwdriver with a rag. Mazda says to wrap it in tape. Hyundai says to use a slim tool and pry gently.
5. 5Step 5: Lift out the old cell and touch nothing else. Toyota says not to move any other part inside the remote or bend the battery terminals. Mazda says to keep off the circuitry.
6. 6Step 6: Fit the new cell. Toyota and Mazda both say the positive side faces up.
7. 7Step 7: Close the cover. Toyota says it should sit with no gaps between the cover and the key.
8. 8Step 8: Test it. Toyota's last step is to press the buttons and check the doors can be locked and unlocked.

Both Toyota and Mazda recommend having the dealer or an expert repairer do the job, because a key can be damaged if it's opened the wrong way. They print the steps for owners anyway.

How do I open my car key fob?

It depends on the key. Some covers pry open at a slot. Some come off only after you press a release and slide out the metal key. The make-by-make table in this guide lists where each key opens, taken from that car's own manual.

Car key battery by make: where it opens and which cell

Each make opens a different way, so match your key to its own manual. This table lists only the cars whose manufacturer manual we read: the Toyota Corolla Hatch, the Mazda CX-5 and the Hyundai Tucson. If your make or year isn't here, the cell and the steps for your key are in your owner's manual.

How do I open a Mazda key fob?

On a 2020 Mazda CX-5, press the knob and take off the lower cover. Press in the tab to release the upper cover. Slide a tape-wrapped flathead screwdriver into the gap, twist, and the upper cover comes away. Lift the cap, swap the CR2032 with the positive side up, then refit the cap and both covers.

How do I change the battery in a Toyota key fob?

On a 2020 to 2021 Corolla Hatch smart key, release the lock and pull out the mechanical key. Remove the key cover with a flathead screwdriver, its tip covered with a rag. Lift out the old CR2032 and fit the new one with the plus side facing up. Toyota notes the key module can stick to the cover and hide the battery.

How do I open a Hyundai key fob?

Hyundai's 2025 Tucson manual gives one move for both keys. Put a slim tool into the slot and gently open the cover. Swap the cell, check it's sitting the right way, and refit the cover. The folding remote key takes a CR2032 and the smart key takes a CR2450, so check which key you have before you buy.

Can I drive my car if the key fob battery dies?

Yes, on the Toyota whose manual we read, and Hyundai gives a similar backup for a smart key that isn't working correctly. The metal key inside the fob still opens the door. A push-button Corolla still starts with the key held against the engine switch. Toyota calls that a temporary measure and says to change the battery straight away.

1. 1Step 1: Take the metal key out of the fob and open the driver's door with it. Toyota's manual says you'll need the mechanical key when the key battery is flat.
2. 2Step 2: Can't see a keyhole? RACV says some newer cars hide it under a cap or cover on the door handle.

• Push-button Toyota Corolla automatic: put the shift lever in P and press the brake pedal, touch the Toyota emblem side of the key to the engine switch, then press the switch. Toyota's manual gives the clutch pedal in place of the brake for a manual car.
• Hyundai Tucson: Hyundai's manual says that if the smart key doesn't work correctly, you press the Engine Start/Stop button directly with the smart key.
• Any other car: look up the flat-key start steps in your own owner's manual.

How do I know my key fob battery is dying?

One sign is range. Toyota and Mazda both list a shorter working range as a sign of a low key battery. Some cars also warn you on the dash when the engine is switched off. And Mazda says the light on the key stops flashing when you press a button.

• Shorter range. Both the Toyota Corolla and Mazda CX-5 manuals list it.
• A dash warning. A Corolla with smart entry sounds an alarm in the cabin and shows a message when the engine is stopped. A CX-5 shows a message for about 30 seconds after the engine is switched off.
• A dead indicator light. Mazda says the light on the key stops flashing when you press a button.
• Nothing happens at all. Mazda says the system stops operating when the buttons are pressed.

Toyota gives the standard key battery life as 1 to 2 years, and says the battery runs down even when the key isn't used. So the spare in the drawer goes flat too. RACV's advice is to change the batteries in both fobs at the same time once the car warns you one is low.

New battery and the fob still doesn't work?

Open the key again and run four quick checks: the cell is the right way up, it's the code your manual lists, the terminals are straight and the cover is fully shut. Anything past that is a troubleshooting job. Our guide to a key fob that is not working picks it up from there.

• Positive side up, as the Toyota and Mazda manuals we read say.
• The same type the manual lists.
• Terminals not bent.
• Cover shut with no gaps.

How do I get rid of the old button battery safely?

Wrap the old cell in sticky tape as soon as it's out, keep it out of reach of children, and take it to a battery recycling drop off point. The ACCC warns that a swallowed button battery can do severe damage within 2 hours, so a loose cell on the bench is a real risk in a house with kids.

1. 1Step 1: Tape it straight away. The ACCC says to put sticky tape around both sides. B-cycle says button battery terminals should be covered in clear tape on all sides.
2. 2Step 2: Put it up high. The ACCC says to store new and used button batteries out of sight and out of reach of young children at all times.
3. 3Step 3: Recycle it. B-cycle is Australia's official battery stewardship scheme and takes button batteries. Its website has a drop off point finder.
4. 4Step 4: Check the key itself. The ACCC says a button battery can come loose if a product is damaged or its compartment doesn't close securely. Toyota says to stop using a key whose cover can't be firmly closed and keep it where children can't reach.

When should I take the key to a locksmith instead?

Take the key to a locksmith when the cover won't open with light pressure, when the case is cracked or won't close firmly, or when the key is still dead after you've fitted the right cell the right way up. Forcing a cover can damage it, and a case that won't shut can let the battery come loose.

• The cover won't lift with light pressure, or a screw or clip won't budge.
• The shell is cracked, or the cover won't close firmly any more.
• The buttons are worn through.
• The key is still dead after a correct swap.
• The metal key is missing from the fob.

ABC Locksmiths does car key batteries and shells from a walk-in shop, and we're an RACQ approved repairer. You'll find car key battery replacement at our Brendale shop at Unit 19, 193-203 South Pine Road, Brendale QLD 4500. If the key is past saving, we can replace a lost or broken car key too.

That review was about a car key that had stopped turning. Bring the key and the car to the counter. Open Mon to Thu 8am to 4:45pm, Fri to 4:30pm. Phone 07 3205 4925.