There are a few "electric riding mowers".
They range in price from about $2,000 to $3,500 (and up).
They are available.
Apparently, way back in 1971,
John Deere manufactured their "Model 90 Eletric Riding Mower"s.
A better alternative is probably a robotic-lawn-mower.
There are several different robotic lawn mowers available through .