Short answer: The number printed on the cell already in your fob beats any chart. Most smart keys take a CR2032; the table below covers the exceptions by make and key style. Pry at the seam notch with a coin, never at a clip. When a new cell does not wake the fob, it needs pairing, $79 to $119, or replacing.
A fob that takes three presses to lock the doors, or works only from a step or two away, is usually asking for a new coin cell. The cell is a few dollars at any parts store. The hard part is picking the right size.
Below is the cell each of the 20 makes we work on usually takes, split by key style, because one make can use three sizes across its lineup. After the table: opening a case without snapping the clip that holds it shut, the swap mistakes that mimic a dead fob, and what to do when a fresh battery changes nothing.
Why the cell in your hand beats any chart
Carmakers change fobs partway through a model's run, share shells between trims and switch suppliers, so a make-level chart can only say usually. The cell you pull out has its size stamped on the face. Read it before you shop, and if the print has worn off, take the old cell to the counter and match it there.
The size code is the same on every lithium coin cell. The first two digits give the width in millimeters and the last two the height in tenths of a millimeter. A CR1616 and a CR1620 share a 16 millimeter width but not a height, and a CR2450 is the wide, thick cell found in some newer, larger smart keys.
Battery by make and key style
Treat this as a starting point, not a parts order. Where a make used more than one cell across its keys, the entry says usually, or says varies where the old cell is a safer guide than any single size. The years are approximate because changeovers happened model by model.
| Make | Key style | Battery |
|---|---|---|
| Toyota | Remote head key, buttons in the key head | Usually CR2016 |
| Toyota | Smart key, through about 2017 | Usually CR2032 |
| Toyota | Thicker smart key on many 2018 and newer models | Usually CR2450 |
| Lexus | Smart key | Varies, check the old cell |
| Honda | Remote head key with a fixed blade | Usually CR1616 |
| Honda | Push-to-start smart key | Usually CR2032 |
| Acura | Smart key | Usually CR2032 |
| Nissan | Intelligent Key (smart key) | Varies, check the old cell |
| Infiniti | Intelligent Key (smart key) | Varies, check the old cell |
| Ford | Remote head key or separate remote | Usually CR2032 |
| Ford | Smart key, about 2015 and newer | Usually CR2450 |
| Ford | Smart key, earlier models | Usually CR2032 |
| Chevrolet | Flip key, separate remote or smart key | Usually CR2032 |
| GMC | Flip key, separate remote or smart key | Usually CR2032 |
| Hyundai | Smart key | Usually CR2032 |
| Kia | Smart key | Usually CR2032 |
| Subaru | Remote head key | Usually CR1620 |
| Subaru | Smart key | Usually CR2032 |
| Mazda | Flip key with fold-out blade | Usually CR1620 |
| Mazda | Smart key | Usually CR2025 |
| Jeep | Fobik dash-slot key or smart key | Usually CR2032 |
| Dodge | Fobik dash-slot key or smart key | Usually CR2032 |
| Ram | Fobik dash-slot key or smart key | Usually CR2032 |
| Volkswagen | Flip key or smart key | Usually CR2032 |
| Audi | Flip key or smart key | Usually CR2032 |
| BMW | Smart key, about 2010 to 2018 | Usually CR2032 |
| BMW | Slot or diamond-shaped key, about 2001 to 2013 | Often rechargeable, no coin cell to swap |
| Mercedes-Benz | Chrome smart key, 2013 and older | CR2025, one or two by key; check the old cells |
| Mercedes-Benz | Newer smart key, about 2014 and later | Usually CR2032 |
Opening the case without snapping the clip
Most fob cases are two plastic halves held by small clips molded into their edges, and those clips are what breaks. A case with a snapped clip gaps, creaks and can shed its battery in a pocket. Before prying anywhere, look for a notch or slot along the seam; that is where the maker expects a tool, away from the clips.
On a smart key, slide the release and pull the emergency blade out first; on many, the slot the blade leaves is the pry point. Use a coin or a plastic trim tool rather than a screwdriver, seat it in the notch, and twist instead of levering. Work a little farther along the seam and twist again. Some cases hide a small screw, so look for one before adding force.
Once the case is open, see which side of the old cell faces you, usually the printed side. Lift it out with a fingernail or a plastic edge; a metal tip can bend the contact tab. Keep the rubber button pad seated, fit the new cell the same way up, and press the halves together until they click evenly all the way around.
Swap mistakes that look like a dead fob
A cell one size too thin often drops into the slot and works on the kitchen table, then loses contact the first time the fob hits the floor. One too thick can crack the case or stress the board when the halves are forced shut. If the fob works only while you squeeze it, the height is wrong or the contact tab has flattened.
An upside-down cell, a button pad left crooked, or a spare cell that sat in a drawer for years all give the same symptom: nothing. Hold the new cell by its edges, check the date on the package, and test every button from a few car lengths back before you throw the old cell away, in case you need its number again.
When a fresh battery changes nothing
If the swap is right and the buttons still do little, the fob may have drifted out of step with the car's rolling code. Many owner's manuals list a short resync routine, and it costs nothing to try before calling anyone.
When the buttons stay dead, either the car no longer lists the fob or the board has failed. A fob the car has dropped needs programming at the car: $79 to $119 with us, against $120 to $200 as dealer labor. A cracked solder joint or water damage calls for replacement: $165 to $259 with us for a remote head key ($300 to $450 from a dealer), and $229 to $399 for a push-button fob ($400 to $750 from a dealer).
If you would rather not open the case at all, we fit the cell at your car for $20 to $45, nearer $20 when the battery rides along with another job, and test every button before leaving. A dealer will fit one for $15 to $30 if you bring the car in and wait.