The more power required, the less time batteries last. For example, if your lawn is lush and thick, or if you let it grow tall before mowing, assume batteries will last for 4,000 to 5,000 square feet or so. If your lawn is easier to mow, many cordless electrics can handle up to 8,000 square feet of lawn. 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.