A 4-gallon backpack sprayer can cover up to 23 tanks on a single charge, depending on the type of sprayer. The Field King 190515 backpack sprayer is ideal for an enthusiastic amateur landscaper and can cover up to 4 hours on a single battery charge. With the right nozzle, you can also adjust the pressure from stream to mist, allowing you to reach farther and cover more area with each tank.