Open the key fob and swap out the old battery

Your Prius key fob battery dies like any other—usually after three to four years of regular use. The replacement takes about five minutes and costs $3 to $8 for the battery itself. You do not need a dealer visit or special tools; a coin or flathead screwdriver is all you need.

Start by locating the slot on the side or back edge of your key fob. This is where the two halves separate. Insert a coin (a dime or penny works) or a small flathead screwdriver into the slot and twist gently. The fob will pop open into two plastic pieces. Do not force it—if it does not budge, you are in the wrong slot.

Once open, you will see a small round battery sitting in a metal holder. The battery is typically a CR2032, which is the standard coin-cell battery used in most Toyota key fobs. Note which side faces up (usually the flat side marked with a + symbol points toward you). Gently pry the battery out using your fingernail or the edge of your coin, then drop the new CR2032 in with the same side facing up.

Key Takeaways

  • Prius key fobs use a CR2032 coin-cell battery that you can buy at any drugstore, grocery store, or hardware store for under $10.
  • The fob opens by inserting a coin into the slot on its edge and twisting gently until the two halves separate.
  • Install the new battery with the flat + side facing up, matching the position of the old one.
  • Test the fob buttons before closing it to make sure the battery is making contact and the fob works.
  • Close the fob by pressing the two halves together firmly until you hear or feel a click.

Test the buttons before closing the fob

Before you snap the fob back together, press each button—lock, unlock, and panic—to confirm the new battery is working. You should see the LED light on the fob flash when you press a button. If nothing happens, the battery may not be seated properly. Lift it out and reseat it, making sure the + side is facing up and the battery sits flat in its holder.

If the buttons still do not work after reseating, the battery itself may be defective (rare, but it happens). Swap it for another CR2032 from the same package or store. Once all buttons light up and respond, you are ready to close the fob.

Close the fob and verify it works with your car

Press the two halves of the fob together firmly until you hear a small click or feel resistance. The fob should be snug and not rattle. If it feels loose, open it again and check that the battery is still seated correctly and that no plastic pieces are out of place.

Stand near your Prius and press the unlock button. Your car should respond with a flash of the lights or a chirp. If it does, the battery change is complete. If your car does not respond, open the fob one more time and confirm the battery is in the right position. A battery installed upside down is the most common reason a fob stops working after a battery change.

Where to buy a CR2032 battery

CR2032 batteries are sold everywhere. Check the pharmacy section of any grocery store, the battery aisle at hardware stores like Home Depot or Lowe's, drugstores like CVS or Walgreens, or online retailers. A single battery costs $2 to $5; a pack of two or four is usually a better value if you have multiple key fobs or devices that use the same size.

Do not buy the cheapest option you see. Batteries from name brands like Energizer, Duracell, or Panasonic tend to last longer than generic store brands. The difference in price is usually less than $1, and a quality battery will power your fob for years.

Common mistakes that prevent the fob from working

The battery is installed upside down. The flat side with the + symbol must face up toward the button side of the fob. If you flip it, the fob will not work. This is the single most common mistake.

The battery is not seated all the way down. If the battery sits at an angle or does not lie flat in its holder, it will not make proper contact. Press it down gently until it sits flush.

The fob was not closed properly. If the two halves are not pressed together firmly, the battery may shift inside and lose contact. Open the fob and close it again with more pressure.

You bought the wrong battery size. Always check your old battery before you leave the store. If the old one says CR2032, buy CR2032. Other common sizes like CR2025 or CR2016 will not fit or work.

When to replace the battery again

A new CR2032 battery typically lasts three to four years in a key fob that you use daily. You will know it is dying when the buttons stop responding from your usual distance—you have to stand closer to the car for the fob to work. At that point, the battery is weak and a replacement is due soon.

If your fob suddenly stops working all at once with no warning, the battery may have failed, but it could also mean the fob itself is damaged or the car's receiver is not working. Try the fob on another Prius if you have access to one. If it works on the other car, your Prius may need service. If it does not work on any car, the fob battery or fob itself needs replacement.

Frequently Asked Questions

Can I use a different battery size if I cannot find CR2032?

No. CR2032 is the only size that fits a Prius key fob. Other sizes like CR2025 or CR2016 are too thin or too thick and will not make contact. Buy the correct size—it is widely available and inexpensive.

What do I do with the old battery?

Take it to a battery recycling program. Most retailers that sell batteries, including Best Buy, Home Depot, and many grocery stores, have free battery drop-off bins near the entrance or customer service desk. Do not throw it in the trash.

Will changing the battery erase my car settings or require reprogramming?

No. The key fob battery is separate from your car's memory. Changing it will not affect your seat position, radio presets, or any other settings. The fob will work when ready after you close it.

How do I know if my fob has a dead battery or a broken button?

Replace the battery first. If the buttons still do not work after a fresh battery is installed correctly, the button contacts inside the fob may be worn out or the fob may be damaged. At that point, you will need a replacement fob from a Toyota dealer or a third-party supplier.

Can I change the battery in a smart key fob the same way?

Prius smart key fobs (the ones you keep in your pocket and do not press a button on) also use a CR2032 battery, but they open differently. Look for a small slot or release button on the edge, or consult your owner's manual for the exact method. The battery swap itself is the same once the fob is open.