Expensive yes, but how is it any less practical than the stock of fossil fuel you currently have to invest in and store, or the staff costs to run? It is just another business model.Stations set up to remove one battery pack and fit a fresh one will be quite expensive to operate.
1. Garage with vehicle lifts, parking, battery storage, bulk battery charging and offices.
2. Staff (wages, holidays and associated costs) Trained staff with 6-8-10 on duty 24 hours a day (fuel station one or two staff). Additional staff if it includes a shop.
It will not be just the cost of the electricity to charge to battery.
Every battery changing garage will need a stock of spare charged batteries so we will need 10 or 12 spare batteries X 8000 garages means 80,000 to 100,000 spare batteries.
Not very practical.
I work in a fuel station on my own and can refuel ( I do the filling not the customer) 100 cars a day and run the shop.
I would expect the the battery changeover would be automated, but even if done on a pitstop basis, the positive of more employment is not to be sneezed at.
It would need to be a battery hire charge and of course that would not just be the cost of the electricity to recharge. I could imagine the changeover and hire cost would likely be at a fixed rate with just the difference in charged states being the variable...the hire charge would include for battery purchase and depreciation as has already been mentioned a few times.
My sister and brother-in-law developed a one man filling station into a business which now employs some 50 or so people by diversifying and re-investment in stock and equipment, so I have an albeit second hand clue as to the practical possibility.