Even when you also figure the cost of battery replacement every 5 to 7 years, cordless electrics can still cost less than gas mowers in annual expenses. The two Lawnboy cordless electric mowers have 6-volt batteries. Power is a function of battery type, blade and deck design, and power transfer. All manufacturers exploit computer-aided design techniques to optimize blades' weight and shape and decks' contours. Expect the batteries to last about 5 to 7 years.
Batteries lose power when they're stored for a long time.
If temperatures generally stay above 40 o F. where you live, leave the battery connected or plugged in year-round. However, check the owner's manual for specific storage directions. How long a machine will run depends on the height and texture of the grass, moisture levels, and the terrain. Cutting relatively dry lawns takes a lot less energy than cutting lush, wet turf. Some mowers come with a separate recharger, a device that stays plugged into an outlet, into which you place the battery pack for recharging.