How many is enough is a complicated thing though. You don't need there to be as many pumps as cars because there is enough everywhere that you know with certainty that you can find one any given time within 15 minutes and be refueled in 5.

If you have a charger or as many chargers at your apartment for the number of electric cars you know you are going to be able to charge with certainty.

If you have some small number of chargers at work do you know that you are going to be able to charge? Are you going to go into work park at the charging spot for 30 minutes then play musical chairs with your coworkers instead of working or are you going to park for 9 hours then leave at approx the same time as others ensuring that exactly 5 cars get charged per week despite being able to theoretically charge 336 per week in 3O minute blocks.

Regarding trips to the grocery store. Did you spend 30 minutes in a parking lot of a grocery store or mall this week? I haven't this month and even so you can't be sure that one of a small number of spots are actually available.

Currently plug in vehicles are what 1.9% of cars on the road. A relatively small number of spots scattered here and there is enough for this to work better than expected but trying to scale this begins to get pretty stupid pretty fast.

What does this look like with 1 in 3 cars? At 2 in 3 cars? How does it look like when you try to put enough chargers in the place where people incidentally land for extended periods of time instead of just putting them in lots of homes and apartments?