How to replace car key battery Most key fobs have a little slot you can use to pop them open with a small flatheaded screwdriver, a butter knife or another key.

Like anything else relying on a battery, you car key fob can die—often at the worst time. Thankfully, these batteries are easy to replace.

The key fob is your lifeline to your car, letting you unlock the doors and set off the alarm, at a minimum, but how can you tell if it needs a new battery?

There’s usually a mechanical key hiding inside the key fob for cars with push-button start systems, so you can still unlock your door if the car battery or your fob battery runs out of juice.