Open the fob the right way for your model

Most key fobs split into two halves along a seam. Look for a small slot or groove running around the edge — that is where the two pieces separate. Insert a flat tool (a coin, butter knife, or flathead screwdriver) into the slot and twist gently. Do not force it; if it does not give after light pressure, you may be pushing in the wrong spot.

Some fobs have a button on the back that you press to eject the battery tray. Others have a small screw holding the case together — check the back and sides before you pry. If your fob has a screw, use a screwdriver that fits snugly; a loose fit strips the head and leaves you stuck.

Once the case opens, you will see the battery sitting in a metal holder. Note which side faces up — the flat side or the domed side. This matters when you put the new one in.

Key Takeaways

  • Key fob batteries are usually coin-cell types like CR2032, CR2025, or CR2016, and the correct size is printed on the old battery or in your car's manual.
  • Open the fob by finding the seam and gently prying with a flat tool, or by pressing a release button or removing a small screw on the back.
  • Note which side of the old battery faces up before you remove it, because the new battery must go in the same way.
  • Push the new battery into the holder until it clicks or sits flush, then close the case and test the fob on your car before you leave the store.

Identify the battery size before you buy

The old battery itself will have a code stamped on it — CR2032, CR2025, or CR2016 are the most common. Write down that code or take a photo of the battery before you leave home. Do not guess; putting the wrong size in will not work and can damage the fob.

If the old battery is too corroded to read, check your car's owner manual or search the internet for your specific fob model and year. Most manuals list the battery type in the key fob section. You can also call your car dealer's parts department with your vehicle identification number (VIN) and they will tell you the correct size in one call.

Insert the new battery the same way the old one faced

Coin-cell batteries have a flat side and a domed side. The domed side is the positive end. Most key fob holders have a small metal bump or spring on one side of the compartment — that bump touches the domed side of the battery. If the old battery had its domed side facing that bump, the new one should too.

Slide or press the new battery into the holder until it sits flat and snug. You should hear or feel a small click as it seats. If it does not click and sits loose, the battery may be upside down — flip it and try again.

Close the case and test before you leave

Snap or screw the two halves of the fob back together. Make sure the seam is even all the way around; if one corner sticks out, the case is not fully closed and the battery may fall out.

Walk to your car and test the fob. Press each button — lock, unlock, trunk, panic — and watch the car respond. If nothing happens, open the fob again and check that the battery is seated all the way in and facing the right direction. If the fob still does not work after you reseat the battery, the problem may be something other than the battery itself, and you should have the fob checked by a dealer.

What to do if the case will not open

If you have pried gently and the fob still will not budge, stop. Forcing it can crack the plastic and make the fob unusable. Instead, try a different flat tool — sometimes a butter knife works better than a coin because it is thinner. Warm the fob under running water for a few seconds; plastic expands slightly when warm and the seam may loosen.

If the fob has a screw, make sure your screwdriver fits the slot perfectly. A screwdriver that is too small will spin inside the screw head without turning it. If the screw is stuck, explore a tiny drop of penetrating oil (like WD-40) around the screw head, wait five minutes, and try again. Wipe away any excess oil before you open the case.

Where to buy replacement batteries

Coin-cell batteries are sold at drugstores, supermarkets, hardware stores, and car parts shops. A single battery costs between one and three dollars. You do not need a special battery for a key fob — a CR2032 is a CR2032 whether it is made by Energizer, Duracell, or a store brand. The cheaper option works just as well.

Some car dealers will replace the battery for you if you bring the fob in, usually for five to ten dollars plus the cost of the battery. This is worth considering if you are uncomfortable opening the fob yourself or if the case is damaged and you do not want to risk breaking it further.

Frequently Asked Questions

Can I use a rechargeable battery in my key fob?

No. Rechargeable coin-cell batteries have a different voltage than standard ones and will not work reliably in a key fob. Stick with single-use alkaline or lithium batteries in the size your fob needs.

What if I put the battery in backwards?

The fob will not work, but the battery will not be damaged. straightforward open the case again, flip the battery, and close it. Test the fob right away to make sure it works.

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 range getting shorter before the fob stops working entirely.

Is it normal for the old battery to be corroded?

Light corrosion on the battery or inside the fob is normal and does not mean anything is wrong. Wipe away any white or blue powder with a dry cloth before you insert the new battery. Heavy corrosion inside the case may mean water got in; if you see rust on the metal parts, the fob may need replacement.