Most car key batteries last three to four years and cost $3 to $10 to replace

A dead car key battery is one of the easiest car problems to fix yourself. You do not need tools, a mechanic, or special knowledge — just the right battery type and two minutes of your time. The battery sits inside your key fob, the plastic remote you use to lock and unlock your car. When it stops working, you can open the fob, swap out the old battery, and close it back up.

The hardest part is finding out which battery your key uses. Car manufacturers use different sizes depending on the model year and brand. Once you know the type, you can buy a replacement at any pharmacy, grocery store, or hardware store for less than the cost of a coffee.

Key Takeaways

  • Car key batteries are coin-cell batteries, usually CR2032, CR2025, or CR2016, and cost between $3 and $10 at any drugstore.
  • You can find your battery type by looking at the number printed on the old battery itself, checking your owner's manual, or searching your car model online.
  • Most key fobs open by sliding a small lever or prying gently at the seam with a coin or flathead screwdriver.
  • Replace the battery with the positive side facing up, close the fob, and test it before you leave the store.

Find out what battery type your key needs

The easiest way is to open your key fob and look at the old battery. The battery itself has a number stamped on it — usually CR2032, CR2025, or CR2016. Write that number down or take a photo with your phone. That is the exact battery you need to buy.

If you cannot open the fob or the battery is too corroded to read, check your car's owner's manual. Search the index for "key fob" or "remote battery" and it will tell you the type. If you do not have the manual, search online for "[your car year and model] key fob battery" and you will find the answer in seconds.

Open your key fob safely

Most key fobs have a small seam running around the edge where the two plastic halves meet. Look for a tiny lever or slot on one side — some fobs have a button you press, others have a small notch you push with your fingernail. Press or slide it and the fob will pop open into two pieces.

If there is no visible lever, use a coin or a flathead screwdriver to gently pry at the seam. Start at one corner and work your way around. Do not force it — if you feel strong resistance, stop and look for a hidden button or lever you may have missed. The fob is held together by a clip, not glue, so it should separate with light pressure.

Once the fob is open, you will see the battery sitting in a small metal holder. It is a thin, round disc, usually silver or gold colored. Note which side is facing up — the positive side (marked with a + symbol) should face toward you.

Remove the old battery and install the new one

Gently pry the old battery out of its holder with your fingernail or the edge of a coin. Do not use a sharp tool that could damage the metal contacts inside the fob. Set the old battery aside.

Take your new battery and place it in the same holder with the positive side facing up, the same direction the old one was facing. Press down gently until it clicks into place. The battery should sit flat and not wobble. If it feels loose, remove it and try again — it may be upside down.

Close the fob and test it

Line up the two halves of the fob so the seam is even all the way around. Press them together firmly until you hear or feel a click. The fob should be snug and not rattle when you shake it.

Point the fob at your car from about 10 feet away and press the lock button. Your car should lock. Press unlock and it should unlock. If nothing happens, open the fob again and check that the battery is facing the right direction — positive side up. Close it and test again. If it still does not work, the battery may be defective, so try a fresh one from a different package.

Where to buy replacement batteries

Car key batteries are sold at pharmacies (CVS, Walgreens), grocery stores, hardware stores (Home Depot, Lowe's), and online retailers. They cost $3 to $10 depending on the brand and where you shop. Name brands like Energizer and Duracell are reliable, but store brands work just as well and cost less.

Buy your battery before you open your key fob so you can test it right away. Most stores will let you open a package and test the battery in the store, then buy it if it works. That way you know you have the right type before you leave.

Common mistakes to avoid

The most common mistake is installing the battery upside down. The positive side (marked +) must face up toward the top of the fob. If your fob does not work after replacement, this is the first thing to check.

Another mistake is buying the wrong battery type. CR2032, CR2025, and CR2016 look almost identical but are slightly different thicknesses. If you buy the wrong one, it will not fit properly or will not make good contact with the metal holder. Always check the number on your old battery or in your owner's manual before you buy.

Do not force the fob open or closed. If you feel strong resistance, stop and look for a hidden button or lever. Forcing it can crack the plastic or damage the circuit board inside.

Frequently Asked Questions

Can I use any coin-cell battery, or does it have to be the exact model number?

It has to be the exact model number. CR2032, CR2025, and CR2016 are different sizes and will not work in a fob designed for a different type. Using the wrong battery can damage the contacts or drain quickly. Always match the number on your old battery.

How long does a new car key battery last?

Most car key batteries last three to four years with normal use. Heavy use — pressing the buttons many times per day — can shorten that to two years. You will know it is dying when the fob only works from very close to the car or stops working entirely.

What should I do with the old battery?

Coin-cell batteries contain small amounts of lithium and should not go in the trash. Take the old battery to a pharmacy, hardware store, or recycling center. Many stores that sell batteries will take old ones back for free.

My key fob has two batteries inside. Do I replace both?

Yes, replace both at the same time. If one is dead, the other is likely close behind. Replacing both ensures your fob will work reliably for the next three to four years.

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

First, open it again and check that the battery is facing the right direction — positive side up. If it is, try a fresh battery from a different package, as the first one may be defective. If a new battery does not work, the circuit board inside the fob may be damaged, and you will need a replacement fob from your car dealer or a locksmith.