Key Fob Battery Type: How to Find the Right Cell
Key fob battery type: how to find the exact cell your remote takes, read the code on the old battery, and use the FCC ID to match a replacement fob.
Key fob battery type, how to find it: open the fob and read the code printed on the battery already inside, because that code is the part number you need to buy. If the old cell is missing or unreadable, check the owner's manual section on the remote or smart key, then look for a marking molded inside the fob case. For a replacement fob rather than a battery, the number that matters is the FCC ID on the back of the remote, together with the maker's part number, not the car's model name alone.
Those are two separate jobs that people often mix up. This guide takes them one at a time: first the battery, then the fob itself and its blade.
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Why the battery code matters more than the car
Two cars from the same brand and the same year can use different fobs, and different fobs can take different cells. The remote for a base trim with a turn key may be a different part from the smart key on a push-button trim of the same model. If you are not sure which version you have, our guide on how to tell what trim your car is covers the reliable ways to check.
That is why a "battery by make" chart is a starting point at best. The cell that is physically in your fob is the one that fits it.
Step 1: Read the code on the old battery
Most car remotes use a lithium coin cell, and coin cells carry their designation stamped on the flat face, usually the positive side. You will typically see two letters followed by four digits, such as CR2032, CR2025, CR2016, CR1632 or CR2450.
Open the fob the way the owner's manual describes. Many fobs have a small release for a hidden mechanical key, and the gap left behind is where the case is meant to be pried. Use a plastic tool or a coin rather than a screwdriver if you can, because the plastic marks easily and some cases have a seal.
Before you lift the old cell out, note which way up it sits. The positive face normally has the code and a plus sign on it.
Step 2: Understand what the code tells you
On common lithium coin cells, the letters describe the chemistry and shape, and the digits describe the size. The first two digits are the diameter in millimeters and the remaining digits describe the thickness. That is why a CR2032 and a CR2025 share the same diameter but are not the same cell: one is thicker than the other.
This matters because a thinner cell can drop into a slot built for a thicker one. It may seem to work, then lose contact when the fob is squeezed or dropped, which feels like a failing fob rather than a wrong battery. A thicker cell forced into a thinner slot can stress the contacts or stop the case closing. Match the full code, not just the first two digits.
Some fobs take two cells stacked together, and some newer smart keys use a larger cell than older remotes from the same brand. The only way to be certain is to read what is fitted.
Step 3: When the old battery is missing or unreadable
If someone has already removed the cell, or the print has worn off, work through these in order:
- The owner's manual. Most manuals include a section on replacing the remote or smart key battery, often with the cell type and a diagram. If you no longer have the printed book, see our guide to getting your owner's manual free, by manufacturer.
- Markings inside the case. Some fobs have the cell type molded into the plastic near the battery holder.
- A second fob for the same car. If the car came with two, the other one should take the same cell, provided it is the same type of remote.
- A dealer parts or service desk. They can look up the fob part number for your vehicle.
A retailer's lookup by make, model and year can help confirm, but treat it as a cross-check. It does not know which remote your car was actually supplied with.
Changing the battery without creating a new problem
A few practical points, in general terms. Your owner's manual has the procedure for your specific fob, and it takes priority over anything here.
- Handle the new cell by its edges. Skin oils on the faces can affect contact.
- Keep the orientation the same as the old cell.
- Check the seal and the clips. A case that does not close fully can let in moisture.
- Test before you leave. Check the lock, unlock and, where fitted, the proximity or push-button start function.
Most fobs keep their pairing with the car through a battery change. If yours stops working after a correct cell is fitted, the manual may describe a resynchronization step for that model. If it does not, a dealer or automotive locksmith is the next stop rather than repeated attempts.
Coin cells are a serious hazard to children
Every loose coin cell in a house is a risk. The US Consumer Product Safety Commission states on its Button Cell and Coin Battery Information Center (read 27 September 2026) that a button cell battery can burn through a child's throat or esophagus in as little as two hours if swallowed. The page says to seek medical attention immediately and to call the National Battery Ingestion Hotline at 800-498-8666 or the Poison Help Line at 800-222-1222.
Change fob batteries away from young children, keep spare cells in their original packaging, and do not leave the old cell on a counter. The CPSC advises placing non-conductive tape over a used battery's terminals and taking it to a battery collection point.
Replacing the fob itself: what the FCC ID is
If the fob is lost, broken, or will not work with a new cell, you are shopping for a remote, and the battery code no longer helps. The number to find is the FCC ID.
Car remotes are radio transmitters, and in the US a certified radio device carries an FCC identifier on its label or case. On most fobs it is printed on the back, sometimes under the battery cover. It usually starts with a short letter or number code followed by a longer string, for example a pattern like "ABC" plus a product code.
The federal rule behind it is 47 CFR 2.926. As published by the Cornell Legal Information Institute (read 27 September 2026), it says the grantee code is assigned permanently to the applicant, and that the equipment product code chosen by the grantee is made of numerals, capital letters or a combination, may include hyphens, and may not exceed 14 characters in total. The rule also says no FCC identifier may be used on equipment to be marketed unless it has been validated by a grant of equipment certification.
In practice, the FCC ID identifies a certified transmitter design. Sellers and locksmiths use it, together with the maker's part number, to match a replacement remote that talks to your car on the right frequency and in the right way.
Why the FCC ID alone is not enough
Matching the FCC ID is necessary, but it does not settle everything:
- The same FCC ID can appear on remotes with different button layouts. A fob with remote start and one without can share a transmitter certification. Match the buttons too.
- The part number matters. Many fobs also carry a manufacturer part number on the case or circuit board. Match both where you can.
- Programming is separate. A matching fob still has to be programmed to your car. Some vehicles allow owner programming by a procedure in the manual; many require dealer or locksmith equipment. The manual is where to check what yours allows.
- The immobilizer is separate. Many keys and smart keys carry a transponder that the car must recognize before the engine will start. That is a security system, and adding a key to it is a job for the dealer or a qualified locksmith.
The blank: blade profile, not battery
If your fob has a flip-out or hidden metal key, that blade is cut from a blank. The blank has a profile that must match your lock cylinders, and the cut must match your car's key code. The FCC ID says nothing about either.
A locksmith or dealer will identify the correct blank from the existing key or from the vehicle. Some will ask for proof of ownership before cutting a key, which is a sensible security step. If you are unsure what your car's documents cover, our article on owner's manual vs service manual explains which of the two books tends to carry what.
Quick checklist
- Battery only: read the code on the old cell, match all four digits, fit it the same way up.
- No old cell: owner's manual first, then markings in the case, then the dealer.
- New fob: FCC ID plus maker's part number plus the same buttons.
- New key: blank and cut from a locksmith or dealer, programming and immobilizer by the same.
Frequently asked questions
How do I find my key fob battery type without opening it?
The owner's manual usually lists it in the section on the remote or smart key. A dealer parts desk can also look up the fob and its cell. Opening the fob and reading the old battery remains the most reliable check.
Can I use a CR2025 instead of a CR2032?
It is not recommended. They share a diameter but differ in thickness, so the thinner cell can lose contact in a slot built for the thicker one. Fit the exact code the fob uses.
Where is the FCC ID on a car key fob?
Usually on the back of the case, and sometimes inside under the battery cover. It is a letter or number code followed by a longer product code.
Does a new battery erase my key fob's programming?
Usually not, but some models describe a resynchronization step in the owner's manual. If the fob still fails with a correct new cell fitted, see a dealer or automotive locksmith.
What should I do if a child swallows a coin battery?
Seek medical attention immediately. The CPSC lists the National Battery Ingestion Hotline at 800-498-8666 and the Poison Help Line at 800-222-1222.
