Working outside you need the best 4 gallon backpack sprayer. 5 gallons are heavy. Hands free and easy to use.
Backpack sprayers make it much easier to work freely over both large and small areas without having to carry tanks and canisters by hand.
Using a battery operated unit elimiates fatigue in the hand, arm, shoulders and back which you will greatly appreciate if you have any significant amount of spraying to do. The continuous pumping action can be very tiring.