Take one out, start it charging on a super charger. 60 minutes later it's ready to be used.
And I really don't get why people stand in line at a Costco for 20 minutes to save 15c gallon. $3 savings for 20 minutes "work"? Is their time really that cheap?
When a battery comes out of a car, it goes on a charger(underground, or wherever). Each charging station starts with 42 batteries(2 extra for good measure) and each spot that a battery sits in wait is a charging station of its own. At minute 0 a battery goes on the charger. After 40 battery changes, one every 90 seconds, an hour has gone by. At this moment the first battery we put on the charger is full, and we have 39 more charging batteries each finishing their charge at 90 seccond intervals in the same order they went in.
In this way, we never run out of batteries.
Of course first they have to change the system to leased batteries so they dont have to give do the whole 'come back for _your_ battery' thing.
You are correct that this only really would work with leased batteries, but this would require owning up to the actual wholesale manufacturing costs of the batteries, depreciated across the number of miles before the battery is no longer practically usable. Tesla stockholders tend to get upset and confrontational when these numbers are discussed, despite that they are easy to determine since the cost of the Panasonic NCR18650A cell, the number used per Tesla (6831), and the lifespan of the cell, are all known.