eBay with Sun Joe has the Sun Joe 2-Gallon 4-Volt Cordless All Purpose Chemical Sprayer (SJ-APS-2G) on sale for $39 - 20% off with coupon code SJNEWYEAR [Exp 1/3] = $31 with free shipping. 

Up to 4 hours of continuous runtime (up to 15 gallons per charge), 20-inch adjustable spray wand.