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?
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