Harley-Davidson key fobs typically use a CR2032 coin cell battery. The CR2032 battery is a common type of lithium coin cell battery widely available at most electronic stores, hardware stores, and online retailers. It's a 3-volt battery that provides power to the key fob's electronics, including the remote locking and unlocking functions. When replacing the battery, ensure you have a new CR2032 battery, and follow the instructions in your owner's manual or consult a Harley-Davidson dealership for guidance on how to properly replace the key fob battery.