How to Replace a Car Key Fob Battery (and What a Garage Charges)

• Most key fobs run on a coin cell battery such as a CR2032 or CR2025, which typically lasts three to five years and can be swapped in a few minutes with a small flat blade.
• A garage fob battery replacement costs about £15 ($20) according to Checkatrade, and Halfords charges £7 ($9) to fit a battery you buy separately.
• A flat fob rarely strands you, as most fobs hide a metal key and most push-button cars have a backup spot to start the engine, but coin cells are dangerous if a child swallows one.

Swapping a Key Fob Battery Takes a Few Minutes and Costs Far Less Than a New Key

You can replace a key fob battery yourself in a few minutes with a small screwdriver and a coin cell that costs a few pounds. Open the fob, note which way up the old battery sits, lift it out, drop in a new one of the same type and snap the case shut. The type is usually printed on the old battery, and Motor1 says most fobs use silver coin cells such as the CR2032 or CR2025. If you would rather not do it, a garage will charge around £15 ($20) according to Checkatrade, which is a small fraction of the cost of a replacement key.

Fobs give plenty of warning before they die. Motor1 lists the signs as reduced range when locking or unlocking, needing to press the buttons several times, dashboard warning messages and intermittent operation. It puts the typical battery life at three to five years, so a fob that has started to misbehave on a car of that age is almost certainly asking for a new cell.

How to Replace the Battery Step by Step

Fob designs differ, so check your handbook for the exact opening method. The steps below follow Tesla’s published guide for its Model 3 fob, which uses a CR2032 and is a good example of how most coin cell fobs work.

First, place the fob button-side down on a soft surface so the case does not get scratched. Pry off the bottom cover with a small flat-bladed tool. Lift the battery away from the retaining clips and take it out. Wipe the new battery clean and handle it only by its edges, then insert it with the positive side facing up. Hold the cover at an angle, line up its tabs with the slots on the fob and press until it snaps into place. Finally, test the fob by locking and unlocking the car.

Many fobs have a small release button or sliding tab that frees a hidden metal key. Motor1 notes that the exact method varies by brand and model, which is why the handbook is the safest place to check. On the replacement cell itself, buy the same code as the old one. A coin cell that does not sit snugly in the clips is a common cause of the on-off behaviour you were trying to cure, so press the new one in firmly and check that it is level.

What to Do If the Fob Is Already Flat

A dead fob does not have to leave you stranded. Motor1 says most fobs contain a metal key inside the housing, released by a small button or sliding tab, which unlocks the driver’s door manually. On some vehicles the keyhole is hidden behind a removable plastic cover, so look carefully around the door handle before you assume there is no way in.

Starting a push-button car with a flat fob works differently by model. Motor1 says many have a backup method that does not rely on the battery. On some models you press the fob against the start button. Others have a designated spot, such as the centre console, a cup holder or a hidden slot under the dashboard, where the car reads a passive chip inside the key. The procedure varies by brand and model, so Motor1 recommends checking the owner’s manual, and it is worth reading that page before you need it.

How to Tell If It Is the Battery or Something Else

The battery is the first suspect, and it is the cheapest to rule out. The symptoms Motor1 describes are all battery symptoms: the fob only works when you stand next to the car, you have to press a button several times, the dashboard shows a key warning, or the buttons work one day and not the next. A fob that stays dead with a fresh battery in it points to a different fault.

Do not buy a replacement key until you have tried a battery. Checkatrade’s figures make the point clearly: a transponder key at £240 ($320) costs 16 times as much as the £15 ($20) fob battery job. Even the cheapest type it lists, a manual key at £160 ($213), is more than ten times the battery price. If the fob is the only one you have, a flat battery is also the moment to think about a spare, as Checkatrade says a locksmith typically charges £50 to £200 ($67 to $267) just to program a key, and that is before the cost of the key itself.

Keep the Old and New Batteries Away From Children

Coin cells look harmless and are dangerous. The Office for Product Safety and Standards says swallowed button batteries can kill a child and that dead batteries can still hold enough power to badly hurt a small one. Car key fobs are on its list of everyday items that contain them. Tesla’s own battery guide carries a blunt warning: “If the coin cell battery is swallowed, it can cause severe internal burns within two hours.”

The Office for Product Safety and Standards advises taking a child straight to A&E if there is any chance they have swallowed a button battery, giving them nothing to eat or drink and not trying to make them vomit, as that could worsen the chemical reaction. Warning signs, which are not always easy to spot, include coughing, gagging, drooling and vomiting. To prevent it, store spare batteries securely out of reach, dispose of dead ones immediately and recycle them properly, and if the fob case is not held shut with a screw, keep it away from small children.

What a Garage or Dealer Charges, and When to Use One

Checkatrade’s 2026 cost guide puts a key fob battery replacement at £15 ($20) and calls it a cheap and easy fix, adding that a dealer doing any reprogramming might cost slightly more. Halfords offers a fitting service in its stores for £7 ($9), though that price does not include the battery. Halfords is open about the limits: a vehicle inspection can decide whether the battery can be replaced in your key, reprogramming sometimes has to be done by a dealer, and access to the vehicle might be needed.

The saving from doing it yourself is real but small, so the main reason to DIY is convenience. The reason to be careful is that the alternative to a fob fix is expensive. Checkatrade gives these ballpark averages, including VAT, for a replacement key: £240 ($320) overall, £160 ($213) for a manual key, £320 ($427) for a remote key, £240 ($320) for a transponder key and £280 ($373) for a keyless entry key. A locksmith typically charges £50 to £200 ($67 to $267) to program a key. Prices are converted at about $1.33 to the pound.

If a new battery does not bring the fob back to life, check that the cell is the right way up and sitting properly in the clips, then try a second fresh battery. If it still fails, the fob itself or its pairing with the car could be the problem, and that is the point to call a dealer or an auto locksmith rather than keep opening the case. A spare key that works is the cheapest insurance, so it is worth testing yours now and replacing the battery before it quits on a cold morning.

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Sources:

• Checkatrade: Car key replacement: Cost breakdown 2026
• Halfords: Replacement key fob batteries
• Motor1: What Do I Do If My Key Fob Battery Dies?
• Tesla: Replacing the Key Fob Battery
• Office for Product Safety and Standards: Button batteries ‘can kill a child’ if accidentally swallowed, says the Office for Product Safety and Standards
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