In the Leaf owners' manual, CH-4 of the 2015 and older manual addresses long-term storage:
If the vehicle will not be used for an extended period of time, charge the Li-ion battery once every 3 months [to 80%, per the 2012 manual]. Do not operate the charging timer repeatedly while the charge connector is connected to the vehicle after the Li-ion battery charging is completed. Doing so may discharge the 12-volt battery.
and on page EV-5 regarding winter:
the Li-ion battery warmer automatically turns on when the Li-ion battery temperature [falls to] -1°F... turns off when the Li-ion battery temperature [rises to] 14°F
I think that the takeaway is, unless the car is stored where temps will dip down to -1F, the battery heater will not turn-on; and if there is any vampire drain without the heater going, then it is not enough to discharge the battery from 80% in under 3 months. This is a huge difference from some other EVs (-Tesla- -cough- -cough-)
I parked my 2017 Leaf S last January outside in the driveway for 5 days:
- low -15F, high -5F
- low -14F, high -6F
- low -13F, high 1F
- low -10F, high 1F
- low 0F, high 6F (heat wave!! you can see why I go on vacation
)
...so I figured there would be some drain. When I returned, I was surprised to find only 2% drop in the SOC. At that rate, the car could sit at -10F for about 3 months and only lose 36% ! My conclusion is that even month-long sub-zero cold weather vampire drain is not much of an issue if you charge the car first. In winter, I'd follow the 2012 manual and charge to 80%, just to be safe. If it were summer, I'd probably only charge to 60%, to be nicer to the battery.
However, one recurring theme in these forums is the "mysterious dead 12v battery." Many owners have found that their 12v accessory battery has gone from happy to completely dead overnight (especially before Nissan fixed some Telematics bugs). I have the S model (no Telematics), and even I have found my battery completely dead for no reason I could discern (one time in 19 months). While this problem is unlikely, I don't think that there would be any harm done by hooking-up a "Battery Minder" or "Battery Tender Junior" trickle charger to the 12v battery while the car is parked. In fact, that's the perfect time to use a desulfating trickle charger, to help restore the 12v battery from the abuse it suffers under the Leaf's charging program.