If your key fob only works when you're standing right next to the car, or you have to press the button three or four times before the doors unlock, the battery inside is on its way out. This is the most common fob complaint we see and it's usually a $5 part, not a $200 problem. Most people can swap it themselves in under ten minutes once they know which battery their fob takes.
What are the warning signs your key fob battery is dying?
A fob battery doesn't fail all at once. It fades, and the symptoms show up gradually over a few weeks before it dies completely.
- Shorter range. You used to unlock the car from across the parking lot. Now you need to be within a few feet.
- Multiple presses needed. You press lock or unlock two or three times before anything happens.
- Dash warning light. Many newer vehicles (Honda, Toyota, Nissan, most GM models) show a "key fob battery low" message on the dash cluster when the signal starts weakening.
- No response at all. The fob is completely dead but the metal key blade inside still opens the door and starts the ignition manually.
- Push-button start struggles. On keyless-start cars, the ignition takes longer to recognize the fob, or you have to hold it right against the start button.
If the fob is totally unresponsive and the backup key blade won't even get you into the car, that's more likely a different issue, worth checking our car lockout service page rather than assuming it's the battery.
How much does a car key fob battery replacement cost?
The battery itself is cheap. A CR2032 or CR2025 coin cell runs $3 to $8 at a pharmacy, battery shop, or hardware store. If you do it yourself, that's the whole cost.
If you'd rather have a locksmith do it, or your fob needs reprogramming after the swap (rare, but happens on some Mercedes and BMW models), typical mobile service runs in the $25 to $45 range for a straightforward battery swap with a shop visit or callout. This is a typical range, not a quote, since pricing depends on the vehicle and whether any reprogramming is needed. See our car key battery replacement page for how that works in Surrey specifically.
Compare that to a full fob replacement, which runs considerably more once you factor in cutting a new key blade and programming it to the car's immobilizer. If the battery swap doesn't fix the problem, that's usually the next step, and our key fob replacement page covers what that actually involves and costs.
Which battery does your key fob actually take?
This is where people get stuck at the pharmacy counter. Most fobs use one of three coin cell sizes, and they are not interchangeable.
- CR2032. The most common size, used in most Toyota, Honda, Mazda, Hyundai, and Kia fobs. It's a 20mm, 3.2mm thick cell.
- CR2025. Slightly thinner than the 2032, used in some Ford, Chevrolet, and older Nissan fobs.
- CR1620 or CR1632. Smaller cells found in some flip-key and smart key fobs, including certain Volkswagen and Audi models.
Check the old battery before you buy a new one. The size is printed right on it. If you can't get the fob open yet, the owner's manual lists the battery type under the key fob section, and it's also often printed inside the fob case near the battery slot.
How do you actually swap the battery yourself?
The process is similar across most makes, though the exact release point on the case varies.
- Find the release. Most fobs have a small slide button, notch, or seam on the back or side. Some require you to slide out the metal key blade first, which then exposes a slot you can pry from.
- Pry it open gently. Use a small flathead screwdriver or a plastic trim tool, not a knife. Work slowly around the seam. Forcing it with too much pressure can crack the plastic housing or scratch it up, especially on older fobs where the plastic has gotten brittle from UV exposure sitting in a sunny car.
- Note the battery orientation. Before you pull the old battery, look at which side faces up (usually the "+" marking). Snap a quick phone photo if you're not sure, since putting it in backwards means the fob won't work at all.
- Swap and snap shut. Press the new battery in, then click the case back together. Test it on the car before you walk away from the counter or workbench, in case the contacts need reseating.
- Reprogram if needed. On the vast majority of vehicles, no reprogramming is required after a battery swap. A small number of European models do need the fob re-synced to the car afterward. If yours doesn't respond normally after the swap, that's a sign it needs reprogramming rather than a battery problem.
When is it worth calling a locksmith instead of doing it yourself?
If the fob case won't open without serious force, if you've already tried a fresh battery and it still doesn't work, or if the car requires reprogramming after the swap, it's worth getting it looked at rather than risking a cracked case or a fob that needs full replacement. Have your key fob and the car's ignition key on hand when you call, since cutting a new key blade or reprogramming a fob both need the original hardware present. Get in touch with Fast Locksmith Surrey and we can tell you quickly over the phone whether it sounds like a battery issue or something bigger. You can also read more about who we are on our about page.
Frequently asked questions
Can a dead key fob battery stop my car from starting?
On push-button start vehicles, yes, a fully dead fob battery can prevent the car recognizing the key and starting. Most cars have a backup method, usually holding the fob against a marked spot on the dash or console, check your owner's manual for the exact location.
How long does a car key fob battery usually last?
Most coin cell fob batteries last one to three years depending on how often you use the fob and the make of car. Fobs that are used constantly for remote start or frequent locking and unlocking tend to drain faster.
Is a weak key fob battery the same problem as a failing ignition?
No, they're separate systems. A weak battery affects the fob's signal, while ignition problems usually involve the key not turning, the car not recognizing the chip, or the ignition cylinder itself. If a fresh battery doesn't fix it, our ignition repair and rekey page covers the ignition side of things.