I recently purchased a battery powered lawn mower. It uses the same type of Lithium-ion cells that Tesla uses. The battery pack has 3 parallel series of 14 cells for a total of 42 cells. The total energy capacity of the battery is about 0.36 kWh. I was able to mow my lawn today using about 0.29 kWh of energy from the battery--it still had 15-25% SOC left. The last time I mowed my lawn with a gas powered lawn mower (10+ years old), it required 0.27 gallons of gas. The energy released by 0.27 gallons of gas is 0.27*33.705 = 9.1 kWh. The gas powered mower required 9.1/0.29 = 32 times the energy of the electric mower to mow my lawn. Gas powered mowers are extremely inefficient!