A hundred years ago, the entrepreneur couldn’t go wrong by getting into the lucrative battery charging business, as shown by this ad in the August 1918 issue of Popular Science.

The unit appears to be a gasoline-driven six-volt 500 watt generator, capable of charging one to seven auto batteries at a cost of 13-15 cents per battery.  The ad reports that autoists would pay $0.75 – $1.50 for the service, meaning that garage owners were clearing $40 – $60 extra profits per month.

The set was available from Hobart Brothers Co. of Troy, Ohio, for $15 down plus nine payments of $20 each.  The company is still in business, today focused on the welding industry.