I am trying to wrap my head around why anyone would get a Smatree or any other charger that is more or less dedicated to one battery type when you can instead get a general purpose charger (like the Goal Zero I linked to) which will charge anything (using the Goal Zero 120V output via the normal Mavic charger) and which has far more capacity.
I have been with professionals when they fly and I can tell you that they all use either the Goal Zero equipment, or equivalent. When you get your next drone, which will have different battery connections, you can continue to use your Goal Zero.