Last May I wrote a post about free charging etiquette. With various discussions with Tesla owners, the overall conclusion is that when charging at a free private charging station, the best etiquette would be to purchase at least some item from the owners, however small.
Some public locations also offer free charging stations. So far in my limited usage, I have seen these free public charging stations in small ecologically concerned towns near public facilities such as town halls and libraries. The intended use is for locals or visitors to charge while at their facility.
Unfortunately a number of folks have figured out that charging is free 24 hours a day, and regularly charge their cars at these facilities instead of charging at home and paying the electricity bills. One municipality I know has decided to change their rules and begin charging electricity for users during the evening and nights when their facilities are closed.
I think most folks know the common courtesy rules around public charging stations. Treehugger wrote a nice post on this following Ford’s lead on charging etiquette. Tesla has kept out of the discussion in general. The only thing I would add to this list is to not abuse the free charging available at public facilities. They are intended to be used only when you are actually using these facilities not as a substitute for charging at home.