Extracting the fluid is already going to be an interesting task (it seems like it'd probably be uneconomical to suck it out with a vacuum). I can see the cars h

Extracting the fluid is already going to be an interesting task (it seems like it'd probably be uneconomical to suck it out with a vacuum). I can see the cars having separate input and output holes. With a clever design in the car you could probably start refilling while you finish emptying. A recharge should be pretty cheap. The national average cost for electricity is ~13¢/kWh, so refilling a 100 kWh battery would only be $13 of energy. Other costs - storage, maintenance, labor, land, etc - add to that, but you still aren't out that much. It's possible that you just pay full price regardless, since they are giving you totally fresh solution. One of the most important things about flow batteries is that they're basically invariant with charge and scale, so almost certainly (until you really hit the dregs - you probably lose voltage at 4%).