How to Change a Battery in a Car Key

Types of Car Key Fobs

There are two basic fob styles used in cars today.

This active key still requires the driver to insert the metal part into the ignition.

Active Fob

With an active fob, a driver can press a button to lock and unlock the car. There may also be a horn alert function to help find your vehicle in a crowded parking lot. Some fobs have additional buttons to unlock the trunk or activate a minivan’s sliding doors.

A driver still needs to insert a metal key into the ignition switch to start the engine. Some active fobs and its buttons are part of the key’s physical structure, while others are small separate electronic devices that typically go on your key chain.

Passive Toyota car key fob

Passive or Keyless Fobs

With a passive fob, the vehicle recognizes a signal from the fob—typically within 15 feet—which unlocks the driver’s side door. When the fob is inside the car, the start button is activated and the driver can start the car without pulling out the fob (or a separate key).

Passive fobs usually have buttons that lock and unlock the car from a distance. These fobs usually don’t need an old-school metal key, but manufacturers typically place a backup physical key inside the fob housing. If the fob battery suddenly fails, a driver can remove the physical key to get into the car and start it up.

The battery needs to be replaced to get the remote electronic fob working again.

Signs of a Failing Car Key Battery

The key fob’s battery can fail without warning. Since a passive fob uses the battery more often, these units tend to wear out faster, often after two years. Here are three signs that your fob might be failing:

• Some fobs emit a red LED signal to indicate it is in use. With a drained battery, this LED light is harder to see or is not illuminated at all.
• As the battery starts to fail, the fob requires you to get closer to the car before it successfully unlocks the door.
• If you have to press the buttons two or three times before activation, the battery energy could be getting low.

If you suspect the fob battery is failing, try your car’s second fob (if you have one). See if the same issues exist. If your spare fob works fine, that is a good sign that your first fob battery is failing.

If you only have one fob, it’s a good move to get a spare, because it can be expensive to replace a fob without having the original. If you have to purchase a new fob, without having a spare to utilize as a clone, expect to pay over $350 for the fob and labor costs. Buying a new fob and programming it using your existing fob will probably cost about $100.

How to Replace a Car Key Fob Battery

Follow these steps to replace a car key battery:

• If you have a passive fob with a physical key as part of the unit, first remove the key from the fob.
• The fob usually has two pieces of plastic that snap together. Use a thin-bladed screwdriver to pry apart the fob along the seam. Many fobs have a small indent where the blade from the screwdriver can start separating the two pieces. Others have a cover over the battery that is secured with a screw that is easily removed with a screwdriver or coin.
• Once the fob is open, you can see the battery. It is often a circular coin-like battery. Replace the battery only with the same battery type. A replacement battery should cost less than $5. Others might look similar but have different voltages or dimensions.
• Be sure to insert the battery in the same orientation as the old battery, with the positive and negative sides correctly placed.
• The two parts of the fob typically snap together easily.
• Test the fob to see if it is functioning correctly. If you doubt the replacement process, check your owner’s manual for specific instructions.

Since a properly functioning car key is critical for the safe operation and security of a car, it is essential that you quickly replace a bad fob battery. Fortunately, the process is a simple five-minute fix that can be done at home without specialized tools.