Most key fobs open with a flat tool and a small amount of pressure

The fastest way to open a key fob is to find the seam between the two plastic halves, insert a flat tool like a coin or flathead screwdriver, and gently twist. The two halves will separate, revealing the battery inside. The battery usually sits in a small metal holder and slides out sideways or straight up, depending on the fob model. Once you remove the old battery, note which side faces up, then slide the new battery in the same way.

Most car key fobs use a CR2032, CR2025, or CR2016 battery — all the same size and shape, just different thicknesses. You can buy replacements at any drugstore, grocery store, or hardware store for between two and five dollars. The whole job takes less than a minute once you have the new battery in hand.

Key Takeaways

  • The seam between the two plastic halves is where you insert a flat tool to pry the fob open.
  • Most car key fobs use a CR2032 coin-cell battery, which you can buy at any drugstore or supermarket.
  • The battery slides into a metal holder and must be inserted with the correct side facing up — usually the flat side faces down.
  • After replacing the battery, snap the two halves back together and test the buttons before you leave the store or your home.

Finding the seam and opening the fob

Look at the edge where the two plastic halves meet. On most fobs, this seam runs around the perimeter, and there is usually a small notch or gap on one side where you can fit a tool. This is your entry point. A coin works well — a penny or dime gives you enough leverage without being too thick. A flathead screwdriver also works if you are gentle.

Insert the flat edge into the seam and twist gently, as if you were opening a paint can. Do not force it. If the fob does not budge after light pressure, try a different spot along the seam — some fobs have a preferred opening point. Once you feel it start to give, the two halves will usually separate with a small click or snap.

Locating and removing the old battery

Inside the fob, you will see a small metal or plastic holder with a coin-shaped battery sitting in it. The battery is usually silver and about the size of a dime. Some holders have a small metal tab you can lift to pop the battery out; others require you to slide the battery sideways or straight up.

Before you remove the battery, look at which side is facing up. Most coin-cell batteries have a flat side and a slightly domed side. The flat side almost always faces down into the holder. Take a photo with your phone if you are unsure — this takes two seconds and prevents you from installing the new battery backwards.

Choosing and installing the replacement battery

The most common battery for car key fobs is the CR2032. If you are not sure which type your fob uses, check the old battery itself — the model number is printed on one side. Take the old battery with you to the store so you can match it exactly. CR2032, CR2025, and CR2016 batteries look identical but have different thicknesses, and using the wrong one can prevent the fob from closing properly.

Slide the new battery into the holder with the flat side facing down, the same way the old one was oriented. You should hear or feel a small click when it seats properly. If the battery does not sit flush or feels loose, remove it and try again — it may be upside down or not fully inserted.

Reassembling the fob and testing

Align the two halves so the seams match up, then press them together firmly until you hear a click. The fob should feel solid and not have any gaps. Press each button — lock, unlock, and trunk if your fob has one — to make sure they work. If a button does not respond, the battery may not be making good contact. Open the fob again, remove the battery, and reseat it.

If the buttons still do not work after reseating the battery, the battery itself may be defective. Coin-cell batteries are cheap, so buying a second one to test is faster than troubleshooting further. If the second battery also does not work, the fob's circuit board may be damaged, and you will need a replacement fob rather than just a battery.

What to do if the fob will not open

Some fobs are glued shut or have a different design that does not use a seam. If you cannot find a seam or the fob does not budge after gentle pressure, stop trying to pry it open — you risk cracking the plastic. Instead, check your car's manual or search online for your specific year, make, and model of car plus "key fob battery replacement" to find instructions or videos for your exact fob.

If your fob is glued or sealed, a car dealership or locksmith can open it for you, usually for ten to twenty dollars. This is worth the cost if you have already spent time trying to open it yourself and do not want to risk breaking it.

Frequently Asked Questions

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

No. CR2032, CR2025, and CR2016 batteries look the same but are different thicknesses. Using the wrong size can prevent the fob from closing or cause the battery to lose contact with the circuit board. Always match the model number printed on the old battery.

What if I install the battery upside down?

The buttons will not work. Coin-cell batteries have a flat side and a domed side, and they only conduct electricity when oriented correctly. If your fob does not work after you close it, open it again and flip the battery over.

How long does a key fob battery usually last?

Most coin-cell batteries in key fobs last three to four years with normal use. If you use your fob frequently — pressing the buttons many times per day — the battery may wear out faster. There is no way to predict exactly when it will die, so keep a spare battery at home.

Is it safe to replace the battery myself, or should I go to a dealership?

Replacing the battery yourself is safe and takes less than a minute. You are only handling a small battery and two plastic pieces. A dealership will charge you thirty to fifty dollars for the same job, so doing it at home saves money and time.