Most key fob batteries come out by sliding or prying open the case
A dead key fob battery is one of the easiest home fixes you can do yourself. The battery sits inside a plastic case that opens one of two ways: either a small slot on the edge that you slide to separate the halves, or a seam you pry open with a coin or flat tool. Once the case is open, you lift out the old battery, note which side was facing up, and drop in a new one the same way. The whole job takes about five minutes and costs between $3 and $8 for a replacement battery.
The hardest part is usually figuring out which type of battery your fob uses. Most car key fobs take a coin-cell battery — the flat, round kind about the size of a dime or nickel. The model number is printed on the battery itself, so once you open the case you can read it and buy the exact replacement. Common types are CR2032, CR2025, and CR2016. If you do not want to open the fob first, check your car's owner manual or search online for your specific key fob model.
Key Takeaways
- Key fob cases open either by sliding the halves apart or by prying the seam with a coin, depending on the design.
- The battery type is printed on the battery itself, so you can read the model number once the case is open and buy the exact replacement.
- Coin-cell batteries for key fobs cost $3 to $8 and are sold at drugstores, supermarkets, hardware stores, and online retailers.
- When you install the new battery, note which side was facing up on the old one and install the new one the same way — the polarity matters.
How to open the key fob case
Look at the seam where the two halves of your key fob meet. Most fobs have either a small slot or a notch on one edge. If you see a slot, insert a coin (a dime or penny works) into it and twist gently — the two halves should slide apart. If there is no slot, use a flat tool like a butter knife, a flathead screwdriver, or even a coin held sideways, and gently pry the seam until the case cracks open. Work your way around the edge if it does not pop open on the first try.
Some fobs are held together with a screw instead of a snap fit. If you see a screw on the back, use a screwdriver that fits snugly into the head — a screwdriver that is too small will strip the screw and make it impossible to open. Once the screw is out, the case should separate by hand or with gentle prying.
Identify and remove the old battery
Once the case is open, you will see the battery sitting in a small compartment, usually held in place by a metal contact or a plastic clip. The battery is a flat, round disc with a + symbol on one side and a − symbol on the other. Before you remove it, take a mental note of which side is facing up — this matters when you install the new one.
Lift the battery straight out. If it is held by a clip, gently pry the clip back first. If the battery is stuck, a tiny dab of rubbing alcohol on the edge can help loosen it, or you can use your fingernail or a plastic tool to nudge it out. Do not use a metal tool that could scratch the battery compartment.
Find the correct replacement battery
Look at the old battery. One side will have a model number stamped or printed on it — something like CR2032, CR2025, or CR2016. Write this number down or take a photo. These are coin-cell batteries, and they are sold at most drugstores, supermarkets, hardware stores, and online. A single battery usually costs $3 to $8, though some stores sell them in multipacks for less per unit.
If the old battery is too worn to read clearly, search online for your key fob model and the word "battery" — most manufacturer websites or owner manuals list the battery type. You can also take the old battery to a store like CVS, Walgreens, or a hardware store and ask an employee to identify it by sight.
Install the new battery
Before you open the new battery package, make sure the case is still open and you have the compartment in front of you. Remove the new battery from its packaging. Hold it so you can see both sides clearly — the + side and the − side. Now look at how the old battery was oriented: which side was facing up? Install the new battery exactly the same way. If the + side was facing up on the old battery, the + side should face up on the new one.
Drop the new battery into the compartment. If there is a metal contact or clip, make sure it sits properly on top of the battery. The battery should sit flat and not rock or shift when you gently press it.
Close the case and test the fob
If your fob opens by sliding, line up the two halves and slide them together until they click. If it opens by prying, press the seam firmly all the way around until you hear or feel a snap. If there was a screw, replace it and tighten it snugly — do not over-tighten, as you can strip the hole.
Press a button on the fob — the lock or unlock button. If the fob works, the light inside should flash or you should hear a beep. If nothing happens, open the case again and check that the battery is sitting flat and oriented the right way. A battery installed backwards will not work at all. If it still does not work after you flip the battery, the fob itself may have a deeper problem, and you should have it checked by a car dealer or a locksmith.
What to do if the case will not open
If you have tried prying and sliding and the case still will not budge, stop and do not force it — you can crack the plastic and make the fob unusable. Instead, take the fob to a car dealer, a locksmith, or a battery store. Many of these places will open the fob and replace the battery for you for $10 to $20, which is still cheaper than buying a new fob. Call ahead to confirm they offer this service.
Some luxury car fobs or older fobs have cases that are glued or welded shut and cannot be opened at home. A professional will know whether your fob can be opened or whether you need a replacement.
Frequently Asked Questions
What if I install the battery backwards?
The fob will not work at all. The battery has a positive and negative side, and they must match the contacts inside the fob. If you press the buttons and nothing happens, open the case and flip the battery 180 degrees so the other side faces up. Test it again.
Can I use any coin-cell battery as long as it is the right size?
No. The model number matters because different batteries have different voltages and chemical compositions. A CR2032 and a CR2025 are close in size but not interchangeable. Always buy the exact model number printed on your old battery.
How long does a key fob battery usually last?
Most key fob batteries last three to four years with normal use. If you use your fob frequently, the battery may wear out faster. Once it dies, you will notice the fob only works when you hold it very close to the car, or it stops working entirely.
Is it safe to throw the old battery in the trash?
Coin-cell batteries contain chemicals and should not go in household trash. Many drugstores, battery retailers, and electronics stores have battery recycling bins near the checkout. Some municipalities also have hazardous waste collection days. Check your local waste authority's website for drop-off locations.
What if the fob still does not work after I replace the battery?
First, make sure the battery is installed the right way and sitting flat. If it is, the problem may be inside the fob — a broken button, corroded contacts, or a dead circuit. A locksmith or car dealer can diagnose the issue and tell you whether the fob can be repaired or needs to be replaced.