Open the key fob case first

Most key fobs split into two halves along a seam that runs around the edge. Look for a small slot or notch on the side — this is where you insert a flat tool to pry the case apart. A coin, a flathead screwdriver, or a plastic spoon handle works. Insert the tool gently into the slot and twist slightly; the case will pop open without force.

Some fobs have a small button or latch you press before the case opens. Check the back or sides for anything that moves. If you cannot find a seam or button, the fob may use a screw instead — look for a tiny Phillips or flathead screw on the back, usually hidden under a sticker or rubber pad. Remove the screw with the matching screwdriver and the case will come apart.

Once open, you will see the battery sitting in a plastic holder or metal clip. The battery is usually round and flat, about the size of a dime or larger. Note which side faces up before you remove it — the positive side (marked with a + sign) should face the same direction when you put the new one in.

Key Takeaways

  • Most key fobs split along a seam; use a coin or flathead screwdriver in the slot to pry the two halves apart gently.
  • Some fobs use a screw on the back instead of a seam, usually hidden under a sticker or rubber pad.
  • Note which side of the battery faces up before you remove it so you install the replacement the same way.
  • Common key fob batteries are CR2032, CR2025, or CR2016; check your owner's manual or the old battery itself to buy the right size.
  • Snap the case back together by aligning the seam and pressing firmly until you hear a click.

Remove the old battery from its holder

The battery sits in a plastic or metal clip that holds it in place. Gently pry the battery up with your fingernail or a plastic tool — do not use a sharp metal screwdriver, which can scratch the circuit board inside. The battery will pop out easily once you lift one edge.

If the battery is stuck, it may have corroded slightly. Wipe the battery holder with a dry cloth to remove any white or blue residue, then try again. Do not use water or cleaning liquid inside the fob.

Check the battery type and size

Look at the old battery itself — the type and size are printed on one side. Common key fob batteries are CR2032, CR2025, or CR2016. The number tells you the size: a CR2032 is larger than a CR2025. Using the wrong size will not fit the holder or will not work.

If the old battery is too corroded to read, check your key fob's owner's manual or search online for your car's make and model plus "key fob battery." You can also take the old battery to a pharmacy, electronics store, or supermarket — staff can tell you the type in seconds.

Insert the new battery correctly

Place the new battery into the holder with the positive side (+ mark) facing the same direction as the old one faced. Press down gently until the battery clicks into the clip. The battery should sit flat and not wobble.

Do not force the battery in. If it does not fit smoothly, you may have the wrong size. Remove it and double-check the type number against what you bought.

Close the case and test the fob

Align the two halves of the case so the seam lines up evenly all the way around. Press the halves together firmly until you hear or feel a click. The case should be snug with no gaps.

If your fob uses a screw, insert it back through the hole and tighten it with the screwdriver. Do not over-tighten, which can crack the plastic.

Test the fob by pressing each button — lock, unlock, trunk, or panic — while standing near your car. If the fob does not work, open the case again and check that the battery is seated properly and facing the right direction. If it still does not work after a second try, the new battery may be defective; try a different one from a different package.

What to do with the old battery

Do not throw the old battery in the trash. Lithium batteries like CR2032 can leak and damage the environment. Most pharmacies, electronics stores, and supermarkets have a battery recycling bin near the checkout or customer service desk. Drop the old battery there for free.

If your area has a hazardous waste collection day, you can also bring the battery there. Check your city or county's website for the schedule.

Frequently Asked Questions

Can I use a different battery size if I do not have the exact one?

No. A CR2032 and a CR2025 look similar but are different thicknesses. Using the wrong size will either not fit the holder or will not make proper contact with the circuit board, and the fob will not work. 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 with normal use. If you use the fob heavily — pressing buttons many times a day — the battery may wear out in two years. You will notice the fob working at shorter distances before it stops working entirely.

What if the fob still does not work after I replace the battery?

First, open the case again and make sure the battery is seated firmly in the holder and facing the right direction. If it is, try a fresh battery from a different package — the one you bought may be defective. If a second new battery does not work, the circuit board inside the fob may be damaged and the fob may need to be replaced.

Is it safe to open a key fob myself?

Yes. Key fobs are designed to be opened by the owner. There is no battery acid or dangerous material inside. The only risk is dropping a small screw or the battery itself, so work over a table or towel so you do not lose pieces.