Well, we would have to compare two similiar mowers, a corded and a cordless, on a similiar lawn with the kill-a-watt plugged into the wall. Here are the black and decker cordless and corded offerings, they are similiar machines:
cordless model:
Black & Decker Power Tools
Amazon Price: $369.99
Battery - 24 Volt, 17-amp hour, sealed lead/acid type deep discharge battery
Motor - 24 Volt, 1200 watt permanent magnet electric motor
Cutting Path - 19 "
Height Adjustment - 1 Touch
Weight - 76 lbs
Cutting Heights - 1 1/2-3 1/2 "
Ideal Property Size - up to 1/3 Acre
(that is optimistic in my experience)
Mulching Capability - YES
Charge Time at 60% - 4 hrs
Charge Time at 100% - 10 hrs
corded model:
Black & Decker Power Tools
Amazon Price: $218.47
Cutting Path - 19 "
Motor - 12.0 Amps @110 volts (1320 watts)
Height Adjustment - one touch
Weight - 52 lbs
Cutting Heights - 1 1/4-3 1/2 "
Mulching Capability - YES
Ideal Property Size - 100' of outlet
(a 100' radius circle is about 3/4 of an acre, but your property isn't in the shape of a circle)