One of the electronic components we take for granted today is the semiconductor diode for use as a rectifier. But even ninety years ago, if you wanted to build your own battery charger, you could do it at home, as shown by these plans from the October 1926 issue of Popular Mechanics.

To charge a six volt battery, this charger used a 12 volt doorbell transformer.  The rectifier consisted of a glass jar containing a solution of borax, with electrodes made of lead and aluminum.  The total cost of all of the parts was said to be $2.50.