Randy said:
The minimum price should mimic home electric rates so that charging in public costs about the same or more as home.
+1
eVgo got their rates just about right in San Diego. First you decide whether or not $15/month is worth it to you for range peace of mind with a rapidly degrading battery. Then if you go for it they could have had the same charger squatting problem if they had set a zero *incremental* cost. But on top of the monthly fee they charge a per minute fee that works out to just about the same price as charging at home during peak TOU rates.
Thus if you don't need the charge there's no incentive to drive out of your way to use an eVgo charger rather than more conveniently charging at home. But if you do need the charge there's no incentive to take excessive risk with your range to save a few pennies at home. You do just as well to charge where you need when you need.
Finally since the fee is per minute instead of per kWh there is a big incentive to unplug and get out of the way as soon as you have what you need, since the fee per kWh goes up sharply after 80%.