I would've guessed bad starter but it's best to start at the beginning and thats the battery. From there, on to the cables and connections and so on. Sounds like you found your issue with the first thing( the battery). Good deal and easy fix. Our premium gas is only 91 Octane here in Cali. It's pretty awful. Probably the same quality as low grade gas from way back when but if you can run 91 or better you should be good. There are other things like if the filter sock on the sending unit in the gas tank has deteriorated and sucked particles into the carb clogging passages. It happens after time. You might be in for a tank cleaning and a carb rebuild to get things right.