Car Key Battery Replacement If your car key fob doesn't work it could be due to a low or dead battery. Replacing the battery of your car key fob is actually very simple, and can be accomplished in a few minutes at home. First, determine what kind cost of a replacement car key battery your device requires. There are many CR2025 and CR2032 3-Volt batteries that are available at hardware stores as well as some electronic retailers. Open the Car Key If you're anything like the majority of us, your vehicle is an integral element of your life. You need it to get to work, school, and to run around for errands. You are probably frustrated when you press the key fob button to unlock your car, but nothing happens. This could be because your car's battery is dead. It's simple to replace the battery in your car key! First, you must check if the battery in your key fob is low. It may happen abruptly or it might become gradually less durable until it stops working at all.