The length of time a fully-charged battery will last varies from one backpack pump to another. For instance, some models with a lithium-ion battery only last a maximum of 1 hour, 45 minutes. However, there are other backpack sprayers with batteries that last longer, some even going to up to 8 - 10 hours. A case in point is the Petra Battery Powered Backpack Sprayer, whose battery lasts up to 8 hours.