There is no definitive answer to this question as it depends on a variety of factors, such as the brand and model of battery, the type of touchless faucet, and how often it is used. However, most batteries in touchless faucets should last for at least one year with regular use. It is important to keep an eye on the battery level indicator to ensure that it doesn't run out of power unexpectedly. If the battery dies while the faucet is still turned on, it can cause water damage to your sink or countertop.