Had this 21 volt back pack sprayer for 5 years and still works.  I never used it as a backback as never was coordinated enough to get it on. Just carry  around by the handle works for me. Can spray at least 3-4 loads on a charge. Maybe more. Never had that much ambition to do more then that at once.

Not perfect as it can drip a little out of the vent in the cover if filled too full. And I cracked the tab that holds the battery door shut off by carrying it around so have to wrap a small bungee strap around it to hold the door shut.   Was $125.00 when i bought 5 years ago so I don't think 150.00 now is too bad.

Flow-Zone / Storm sprayer