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%.
Beginning in either 2014 or 2015, the 12 volt charging algorithm was improved. 12 volt battery issues are mainly found with pre-'14 Leafs.