I have real nice ‘83 D-150 that is my summer time driver, from April to November and a beater 240K mile 96 GMC Sonoma that is my winter daily driver, typically from December to March. Each one gets filled with Indiana ethanol gas then sets during the down months.
I do add Stabul fuel stabilizer and have never had a fuel issue on either vehicle. Ran these trucks this way since 2011. I too have heard the story that ethanol gas can go bad in a month. So maybe the Stabul makes a difference. But it could be another urban legend. Mainly because it would be easy to do,,,,
I would fix the battery charge issue and drive the Duster daily till I used the fuel in the tank up. Put in fresh and see if the mis fire goes away. The old ignition wiring could also be the issue. So if running fresh gas does not fix it, give it a good tune up, spark plugs, wires, cap, rotor,,,