The 18650 batteries have a long shelf life so long as they are keep at room temperature. You would have no problem ordering them and have them for when you need them. I use the KPT 2s and I have 1 Nautilus. The KPT2s hold 2.5-3 ml of juice. I fill mine to the absolute limit just before it can drip down the tube. I use my rebuilt coils in my KPT tanks with the Areo base. I get great flavor and good vapor from them. The Nautilus I have gives me about the same the KPTs with my rebuilt coil heads IMO. Not sure on the Provari life span but I do know there are people on the board that have had theirs for a long time. They are a very well made unit.