Open the fob without breaking it

Most key fobs split into two halves along a seam that runs around the edge. Look for a thin slot or groove on the side — that is where you insert a flat tool to pry the case apart. A coin, a butter knife, or a plastic spoon works; avoid a sharp screwdriver, which can slip and scratch the plastic or your hand.

Insert the flat edge into the slot and twist gently. You are not forcing it open — you are just creating enough pressure to separate the two halves. The fob will pop apart with a small click. Set both pieces on a clean surface so you do not lose the small spring or contact plate that may fall out.

If your fob has a screw instead of a seam, use a screwdriver that fits the slot exactly — a Phillips head or flathead, depending on the fob. Turn counterclockwise until the screw comes free. Some fobs have one screw; others have two. Remove all of them before you try to open the case.

Key Takeaways

  • The battery type is printed on the old battery itself — usually CR2032, CR2025, or CR2016 — so check before you buy a replacement.
  • The battery sits in a metal holder with a plus side facing up; note which way it goes before you remove it, or take a photo.
  • Slide the old battery out sideways rather than pulling straight up, which can damage the metal contact.
  • A new battery costs between $3 and $8 and lasts three to four years depending on how often you use the fob.

Remove the old battery and note its position

Once the fob is open, you will see a small coin-shaped battery sitting in a metal holder. Before you touch it, look at which side is facing up — the plus sign or the minus sign. Take a photo with your phone if you are not sure you will remember. The battery must go back in the same direction, or the fob will not work.

Slide the battery out sideways using your fingernail or a plastic tool. Do not pull it straight up, because that can bend or break the metal contact underneath. If the battery is stuck, try sliding it in the opposite direction first — sometimes it comes out easier that way.

Look at the battery itself. The type is printed on the flat surface — you will see something like "CR2032" or "CR2025". Write this down or take a photo. This is the number you need when you buy a replacement.

Buy the correct replacement battery

The most common key fob battery is the CR2032, which you can find at any drugstore, supermarket, or hardware store. CR2025 and CR2016 are also common. Do not guess — the wrong size will not fit or will not power the fob.

A single battery costs between $3 and $8 depending on the brand and where you buy it. Buying a pack of two or four costs less per battery than buying one. Duracell, Energizer, and store brands all work the same way; the difference is mainly price and how long they last before the fob stops responding.

Check the expiration date on the package. A battery that expired years ago may not hold a charge. If you are buying online, add a few days to your timeline — the fob will not work until the battery arrives.

Insert the new battery the same way the old one went in

Slide the new battery into the metal holder with the plus sign facing the same direction as the old battery was facing. Push it in sideways until it sits flat and clicks into place. You should feel a small resistance as the metal contacts grip the battery edges.

Do not force it. If the battery does not slide in smoothly, you may have the polarity backwards — flip it over and try again. If it still does not fit, check that you bought the correct size.

Close the fob and test it

Line up the two halves of the fob so the seam is even all the way around. Press down firmly until you hear or feel a click. If your fob had a screw, insert it back into the hole and turn clockwise until it is snug — not so tight that you strip the plastic, just tight enough that it does not rattle.

Point the fob at your car and press a button. You should see the lights flash or hear the locks click. If nothing happens, open the fob again and check that the battery is sitting all the way in and facing the right direction. If the battery is in correctly and the fob still does not work, the problem is likely inside the fob itself, not the battery.

If the fob works, you are done. The new battery will last three to four years in most fobs, depending on how often you use it. Mark the date on your calendar so you remember when to replace it again.

What to do if the fob still does not work

If you installed a new battery and the fob still does not respond, the issue is usually one of three things: the battery is not making contact with the metal holder, the contacts inside the fob are dirty, or the fob's circuit board is damaged.

First, open the fob again and make sure the battery is pushed all the way in and facing the correct direction. If it is, remove the battery and look at the two metal contacts inside the holder — they should be shiny. If they look dark or corroded, clean them gently with a pencil eraser or a dry cloth, then reinsert the battery.

If the fob still does not work after cleaning the contacts, the circuit board inside is likely damaged and the fob will need to be replaced. This is not something you can fix at home. Contact your car's manufacturer or a locksmith to order a new fob.

Frequently Asked Questions

Can I use a different battery size if I cannot find the exact one?

No. A CR2032 and a CR2025 look similar but are different thicknesses, and using the wrong one can prevent the battery from making contact with the holder. Always buy the exact size printed on your old battery.

How long does a key fob battery last?

Most key fob batteries last three to four years. If you use the fob many times a day, it may last only two years. If you use it rarely, it may last five years or longer. When the fob starts to respond slowly or only works when you hold it close to the car, the battery is dying.

Is it safe to replace the battery myself?

Yes. The battery is not dangerous and the voltage is too low to cause injury. The only risk is breaking the plastic case if you pry too hard, so use a flat tool and go slowly.

What should I do with the old battery?

Most retailers that sell batteries also collect old ones for recycling. Take the old battery back to the store where you bought the new one and ask where the recycling bin is. Do not throw it in the trash.

Why does my fob need a battery if my car is running?

The fob sends a radio signal to your car, and that signal requires power from the battery inside the fob. The car's engine does not power the fob — only the small battery does. That is why the fob stops working when the battery dies, even if the car is running.