I have left my 2015 LeafS unplugged, outdoors, in Texas heat, for 5 weeks, for 4 consecutive years. Upon my return, car has started and run normally without issues. State of charge? Once was at 100%, 3 times 50-60%.
It DID require a new 12V battery in January of 2019, when I replaced the OEM battery with a Bosch AGM. When the battery failed, it actually failed to TURN OFF, made a buzzing sound (from the dash somewhere), and then totally failed...no lights of any kind. After replacement, the first start-up interesting, as the dash made several buzzes/clicks/whirrs...
Maybe this helps? You might have killed your 12V battery. If it's an OEM style battery, have you checked electrolyte levels?
2013 Ford Cmax
2014 Toyota Avalon Hybrid Limited
2017 Ford Fusion Hybrid Energi