A century ago, there was big money to be made in charging batteries, and this ad in the November 1921 issue of Science & Invention told you how to get started. For just $20 down, you could purchase from Hobart Brothers Co. of Troy, Ohio, a battery charger.

The company would recommend the size of charger, from 6 to 70 batteries, to make the most money, and you could get started right away. The profits would allow you to pay the easy terms for the balance of the equipment’s price.