What is the difference between the FLEXiO 3500 and the FLEXiO 3550 18V Cordless sprayer?

The FLEXiO 3500 sprayer comes with a convenient on/off switch, a nine speed setting X-Boost turbine, the iSpray Nozzle, and the Detail Finish Nozzle.

The FLEXiO 3550 18V Cordless sprayer comes with a five speed setting X-Boost turbine, the iSpray Nozzle, the Detail Finish Nozzle, an 18V battery, and charger.