And to answer the question: Franklin invented the convention of labeling batteries (in his case, Leyden jars) with the symbols + and -, as he was of the opinion that electricity was a flow from a surplus to a deficit. Of exactly what this surplus consisted of or what actual direction it flowed, he didn't know. Given a fifty-fifty chance, he guessed.
It wasn't until over a 100 years later that the idea of electricity being the a charge was introduced. and almost 150 until the term "electron" was coined for the elementary charge of electricity.
At the end of the 19th century a negatively charged particle that fit the bill was discovered and was named the electron.