I'm Anthony Calhoun, ASE Master Tech. Replacing a key fob battery is the easiest car repair you'll ever do. It takes less than 5 minutes, costs under $8, and requires no tools beyond a small screwdriver or coin. Yet I've seen people pay the dealer $50-$75 for this same 2-minute job. Let me show you how to do it yourself.
Signs Your Key Fob Battery Is Dying
- Reduced range: You used to unlock the car from 30 feet away. Now you have to stand right next to it.
- Intermittent operation: The buttons work sometimes but not others. You have to press them multiple times.
- "Key Battery Low" message: Your dashboard displays a warning. This usually gives you 2-4 weeks before complete failure.
- Delayed response: There's a noticeable lag between pressing the button and the car responding.
Don't ignore these signs. A completely dead fob means you can't use keyless entry, and while you can still start the car, the backup method is inconvenient. For more straightforward guides on car maintenance that any driver can follow, APEX Tech Nation's article library covers everything from batteries to brakes.
What Battery You Need
The vast majority of key fobs use one of these coin cell batteries:
| Battery | Common Vehicles |
|---|---|
| CR2032 | Toyota, Honda, Ford, Chevy, Hyundai, Kia, BMW, Mercedes |
| CR2025 | Some Toyota, Lexus, Honda, Nissan |
| CR1632 | Some Mazda, Subaru |
| CR1620 | Some older Honda, Acura |
If you're not sure, open the fob and look at the battery inside — the type is printed on it. Or check your owner's manual. You can buy these at any drugstore, Walmart, Amazon, or auto parts store for $3-$8.
How to Replace It
- Find the seam. Look at the edges of your fob for a gap or a small notch where the two halves meet.
- Pry it open. Insert a small flathead screwdriver, a butter knife, or a coin into the notch and twist gently. The halves should pop apart. Some fobs have a release button or a slide mechanism — check your manual if prying doesn't work.
- Note the battery orientation. Before removing the old battery, look at which side faces up — usually the + side. Take a photo with your phone if you want to be safe.
- Swap the battery. Pop out the old one and press in the new one in the same orientation.
- Snap it back together. Align the halves and press firmly until they click.
- Test. Stand next to your car and press lock and unlock. Test the trunk button too. Everything should work immediately — no reprogramming needed.
Tips by Brand
Toyota/Lexus: Remove the physical key from the fob first (there's a release button on the back or side). Then pry the two halves apart. CR2032 on most models.
Honda/Acura: Slide open the back panel or use a small screwdriver on the seam. Be gentle — the plastic is thin.
Ford/Lincoln: On the smart key fob, pull the key blade out, then use it to pry the fob open at the notch on the side.
Hyundai/Kia: Remove the metal key, then use a flathead screwdriver in the slot where the key was stored to pry it apart.
BMW: Slide the key blade out of the fob, then insert a small screwdriver where the blade was stored and twist to pop the back cover off.
What to Do If the Fob Is Completely Dead
If the battery died before you could replace it, here's how to start your car:
- Push-button start vehicles: Hold the fob directly against the start button (or a designated spot on the steering column). The car has a short-range reader that can detect the fob even with a dead battery. While holding the fob there, press the brake and hit the start button.
- Physical key backup: Most fobs have a metal key hidden inside (press the release button to extract it). Use it to unlock the driver's door manually. Then use the fob-to-button method above to start the car.
- Key slot vehicles: Some vehicles have a hidden key slot near the steering column, under a panel, or in the center console. The fob physically inserts into this slot to start the car.
Replace the battery as soon as possible after using any backup method.
Disclaimer: This guide covers most common key fobs. Some luxury and specialty vehicles have unique fob designs. Consult your owner's manual for vehicle-specific instructions.