We chose the CR2032 lithium battery for our unit as it is the biggest of the available lithium batteries and also extremely common and inexpensive. This battery is commonly found in bathroom scales, some watches, and various wall clocks. Even with constant use, this battery will last between 9 months to 1 year in our unit. It is extremely easy to replace, and you will know it needs replacing when you notice the screen on the unit goes blank and displays nothing at all. Since the unit is always on and ready for a user, by default displaying the 30 seconds at all times, if the screen is ever blank, the battery has died and needs replacing.