These twelve makers’ manuals give much the same steps: take out the mechanical key, pry the case open at its slot with a wrapped flat screwdriver, fit a new coin battery of the same code the same way up, and close the case firmly.
Match the code on the old battery
The code is printed on the old battery and given in your owner’s manual. Toyota and Mazda both say to replace it only with the same type or an equivalent, and Toyota warns that the wrong type may explode. The battery for each brand and model is on What battery does my key fob take?
The steps the makers share
- Take out the mechanical key. The Toyota, Nissan, Honda, Hyundai, Subaru and Jeep manuals read, Mercedes-Benz’s C-Class Saloon manual, and some Kia and Ford ones, start by taking out the mechanical key.
- Pry the case open at its slot or seam. Toyota, Nissan, Subaru and Mazda say to wrap the screwdriver in a cloth, rag or tape so it doesn’t mark the case. Jeep and Chevrolet manuals also allow a coin, Ford’s 2025 F-150 manual uses a thin coin, Kia’s a slim tool and Tesla’s a small flat-bladed tool.
- Note which way up the old battery sits. Many keys take it positive side up, but GM puts it toward the back cover or facing down in some keys, Nissan toward the bottom of the lower part, Subaru’s transmitters negative side up, and Ford’s Escape (New Zealand edition) manual + facing downward.
- Hold the new battery by its edges. Nissan says holding it across its contacts drains it, Jeep that skin oils can make it deteriorate, and Tesla that finger marks on its flat surfaces can reduce battery life.
- Close the case fully, with any seal or mat in place. GM says a transmitter that isn’t put back together properly can let liquids in.
- Press a button to check it works, as Toyota’s and Nissan’s steps end.
What the makers say not to do
Nissan says touching the internal circuit and electric terminals could cause a malfunction, and GM that static from your body could damage the transmitter. Toyota says not to bend the battery terminals or move other parts, and to work with dry hands, as moisture may rust the battery. The Ford manuals read say not to wipe off any grease on the battery terminals or on the back of the circuit board.
Mazda recommends having its keys done at an Authorized Mazda Dealer, to avoid damage, and Mercedes-Benz’s C-Class Saloon manual a qualified specialist workshop. A wrongly placed battery can drain and leave the key unusable, Kia and Hyundai add.
If the key battery dies first
Each of these manuals gives a way to start the car when the key’s battery is dead.
| Maker | What the manual says | Manual |
|---|---|---|
| Toyota | Touch the Toyota emblem side to the engine switch | 2024 Camry |
| Honda | Touch the H logo to the center of ENGINE START/STOP, buttons facing you | 2023 CR-V (Canada) |
| Nissan | Touch the ignition switch with the Intelligent Key | 2023 Altima |
| Hyundai | Press Engine Start/Stop directly with the smart key | 2025 Tucson |
| Kia | Press ENGINE START/STOP with the smart key, at a right angle | 2026 Carnival |
| Subaru | Touch the push-button ignition switch, buttons facing you | 2023 Outback and Legacy |
| Mazda | Line up the emblem’s center with the push button start | 2024 CX-5 |
| Chevrolet | Put the transmitter in the cupholder | 2022 Equinox |
| Jeep | Push the fob’s nose against START/STOP | 2023 Cherokee |
| Ford | Put the remote in the backup slot, buttons facing the rear | 2025 F-150 |
| Tesla | Scan the key fob on the card reader on the driver’s side door pillar | Model 3 (2024+) |
Toyota calls its procedure a temporary measure and recommends replacing the battery straight away. It also says to carry the mechanical key with the electronic key, since it opens the driver’s door when the battery is depleted.
Steps for your brand
Each brand page has the battery by model and that maker’s own steps.
Keep coin batteries away from children
Toyota, GM, Honda, Jeep, Tesla and Mercedes-Benz all warn in their manuals that a swallowed key battery can cause severe burns, and Toyota, Jeep, Tesla and Mercedes-Benz say within two hours. Hyundai’s 2025 Tucson manual says a swallowed lithium button battery can cause severe or fatal injuries within 2 hours, and Ford’s Escape (New Zealand edition) and Explorer (electric, UK edition) manuals say in two hours or less. Keep new and old batteries out of reach.
The National Capital Poison Center says that if anyone swallows a battery, immediately call the 24-hour National Battery Ingestion Hotline at 1-800-498-8666 or your poison center at 1-800-222-1222. Don’t delay. Immediate treatment decreases severity.