The cars were advertised as reliably getting 80 miles (130 km) between battery recharging, although in one test a Detroit Electric ran 211.3 miles (340.1 km) on a single charge. Top speed was only about 20 mph (32 km/h), but this was considered adequate for driving within city or town limits at the time.

From Wikipedia

Consider that the (in electric cars, obviously next-)most power hungry item on cars back then was the wind shield wiper motor. Modern cars easily put out 100kW, but then spend most of that in a thousand little ways. Back then, a 20W engine would be plenty.