Most car key batteries are coin cells you can swap yourself in under a minute

A dead car key battery is one of the easiest car problems to fix yourself. The battery inside your key fob is almost always a coin-cell battery — a small, flat, round battery that costs between $3 and $8 and takes no tools beyond a flathead screwdriver or a coin. You can buy the right battery at any pharmacy, grocery store, or hardware store, and the swap takes longer to describe than to do.

The challenge is knowing which battery your key uses. Different car manufacturers use different sizes and types. A Honda key uses a different battery than a Toyota key, and a Nissan key uses yet another. The battery type is usually printed on the battery itself once you open the key, but you can also find it in your owner's manual or by searching your car's year, make, and model online.

Key Takeaways

  • Car key batteries are coin cells that cost $3 to $8 and are sold at pharmacies, grocery stores, and hardware stores.
  • You need to know your specific battery type before you buy — common types include CR2032, CR2025, and CR2016, and the wrong size will not fit.
  • Opening the key fob usually requires a flathead screwdriver or a coin inserted into a slot on the edge, not a special tool.
  • Once open, note which side of the battery faces up before you remove it, because the new battery must go in the same way.
  • If your key still does not work after replacing the battery, the problem is likely the circuit board or button contacts, not the battery.

Finding out which battery your key needs

The fastest way is to open your key fob and look at the old battery. Once you pry it out, the battery type is stamped on top — usually something like CR2032, CR2025, or CR2016. Write that number down or take a photo, because you will need it to buy the replacement.

If you do not want to open the key yet, check your owner's manual. Most manuals have a section on key fob maintenance that lists the battery type. You can also search online for "[your car year, make, model] key fob battery type" and find the answer in seconds.

Do not guess. Coin-cell batteries come in many sizes that look similar but do not fit the same slot. A CR2032 is thicker than a CR2025, and a CR2016 is thinner than both. Putting the wrong battery in the fob will not damage anything, but it will not work, and you will have wasted money and time.

How to open your key fob

Most key fobs have a small slot or seam running around the edge. Insert a flathead screwdriver, a coin, or a butter knife into that slot and twist gently. The fob will usually split into two plastic halves. If you cannot find a slot, look for a small button on the back — pressing it sometimes releases a battery cover without opening the whole fob.

Do not force it. If the fob does not budge after gentle pressure, you may be pushing in the wrong place. Try rotating the fob and looking for a seam you missed. Some fobs have the seam on the side rather than the edge, and some have it on the back.

Once the fob is open, you will see the battery sitting in a small plastic holder. It is usually held in place by nothing — it just sits there. Some fobs have a tiny metal clip over the battery, but most do not.

Removing and replacing the battery

Before you touch the old battery, note which side is facing up. The side with the + symbol should be facing either up or down depending on your fob's design. Take a photo if you are not sure, because putting the new battery in backwards will prevent the key from working.

Gently pry the old battery out with your fingernail or the edge of the screwdriver. It should come out easily. If it is stuck, do not dig at it — a little gentle rocking usually frees it.

Drop the new battery into the same spot, with the + side facing the same direction as the old battery did. Close the fob by pressing the two halves together until you hear a click. Test the key on your car door or trunk to make sure it works.

What to do if the key still does not work

If the key does not work after you replace the battery, the problem is not the battery. The most common culprit is dirty or worn button contacts inside the fob. Over time, the rubber buttons wear down or collect dust, and the electrical connection fails even with a fresh battery.

You can try cleaning the contacts yourself. Open the fob again and look at the rubber button pad — it has small metal circles on the underside. Rub those circles gently with a pencil eraser or a cotton swab dampened with rubbing alcohol. Let it dry completely, then close the fob and test it.

If cleaning does not work, the circuit board inside the fob may be damaged. At that point, replacing the entire fob is usually cheaper than repairing it. A new fob from a dealership costs $200 to $500, but aftermarket fobs from online retailers cost $30 to $100 and work with most cars. Your car's owner's manual or a dealership can tell you which aftermarket fobs are compatible with your model.

Where to buy the battery

Coin-cell batteries are sold everywhere. Pharmacies like CVS and Walgreens stock them in the health and beauty section or near the checkout. Grocery stores usually carry them near the pharmacy or in the electronics aisle. Hardware stores like Home Depot and Lowe's sell them in the electrical section. Walmart and Target carry them in multiple locations.

Online retailers like Amazon sell them in bulk packs, which is useful if you have multiple key fobs or want to keep spares on hand. A single battery at a pharmacy costs $5 to $8, but a pack of 10 online costs $10 to $15.

Make sure you have the battery type written down before you go to the store. Telling a cashier "I need a battery for my car key" will not help — you need to say "I need a CR2032" or whatever type your key uses.

Frequently Asked Questions

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

It has to be the exact type. CR2032, CR2025, and CR2016 are all different sizes and will not fit the same slot. Using the wrong battery wastes money and does not work. The number on your old battery tells you exactly what to buy.

What if I lose the old battery before I can read the type?

Check your owner's manual — it lists the battery type. You can also call your car's dealership with your vehicle identification number (VIN), and they will tell you. Searching online for your car's year, make, and model plus "key fob battery" also works.

Do I need to reprogram my key after changing the battery?

No. Changing the battery does not erase any programming. Once you close the fob, it should work when ready. If it does not, the problem is not the battery replacement — something else is wrong with the fob.

How long does a car key battery usually last?

Most coin-cell batteries last three to four years with normal use. If you use your key fob frequently, the battery may wear out sooner. If you rarely use it, it may last longer. There is no way to predict exactly when it will die.

Is it dangerous to have a dead key battery?

No. A dead key battery just means your remote lock and unlock do not work. You can still unlock your car with the physical key blade that is usually hidden inside the fob. You can also start the car normally if you have a push-button start — the key fob is only for remote access.