But if you just look at city operation, situation and solution can be different: Assume having current-gen electric city cars (that's what curren-gen e-cars essentially are) handle a day of a-bit-above-normal use in the city just fine without running out of juice. In that case you just need to charge them overnight (i think Dave or someone else mentioned it already).
And that is the good thing (from technological point of view) regarding cities: You can equip basically every parking lot/house/bunker with charge points. Getting electricity and charge terminal to these places shouldn't be a problem.
The problem here will be how to do the billing. Because nothing will really start moving on a large scale unless all involved parties have agreed upon billing...
We could also have every parking lot and garage equipped with a fuel pump and reservoir, but we didn't do that either. It's a waste of resources, in my opinion. Why install a massive amount of charging stations that are probably not used for most of the time anyways? Plus, just the stations alone isn't enough, the whole issue of power distribution is very important here. After all, EV's dont't just use a hand full of AA cells that need to be recharged. We are talking about kW's of power for just a single car. It _may_ work in some suburban area with a low population density, but just imagine inner city, big houses with, lets say, 40 people wanting to recharge their cars. And the same for the next house, and the next, etc.
I think it is a much better use of resources to equip the gas stations with beefy power lines and have the charging done there.
Having only dedicated "hot spots", like gas stations, equipped with recharge terminals is not a good idea to grow e-car user base in urban concentrations (i don't think anyone will go down this route anyhow). Let me explain...
As said above, we didn't put fuel pumps all over the place either, but use a dense network of gas stations. And hey, it works!
On a gas station you spend 3-5 minutes refuelling and paying (might vary from country to country due to how much petrol/minute goes through the nozzle).
If recharging an e-car (to whatever amount to keep the e-car usable) takes substantially more time, you will see cars piling up at the ramp to the "gas/recharge station" waiting to be recharged. Think about a petrol gas station with petrol cars piling up at rush-hour and multiply this according to the required average recharge time. Uh... not good...
Yes, and that is why i think that using a gas-station like network where you simply pop in a new battery is far better. True, sometimes you will get a pile up, as is the case with petrol cars. But that situation already exists, so having the same for EV's to get a fresh battery is neither worse nor better. Plus, again, i strongly suspect that the battery lifetime will be longer if they are recharged properly under controlled conditions (and maybe properly discharged first if there is any charge left in them, if needed). Also, it would be much easier to spot faulty batteries, or units that are close to the end of their life, and have them replaced in bulk, instead of having the average Joe figuring out what's going on.
Keep in mind that we are talking about EV's being a suitable replacement for petrol cars, and hope to get a really widespread use of them. For only a "few", your proposal might be OK, but i just can't see that working on a more massive scale.
Also, there are many cases where a local charging station is pretty much not feasible at all. People don't always have fixed usage times for their cars. What about cars that are shared amongst family members? Then you are left with very little time for plugging it into the charger. So you end up with a half empty battery that is, at best, topped up only slightly (and thus still not fully charged) before it is used the next time. And what about stuff like public transport, taxis, police cars, firefighter trucks, etc? They all depend on being able to be refueled very quickly, since they are in use for very long times at once.
Oh, and another benefit of a gas-station like battery-swap system: since those stations would use a lot of electricity, they are in a position to get much better prices for the electricity. Of course it is doubtful that the end consumer will benefit from that price-wise, but instead be used to just increase the profit of the station owner. But then, this might be a good incentive for them to establish such a system.
Greetings,
Chris
Edit: Of course that is not to say that EV's should have no means of being recharged and only allow swapping the battery. That should still be possible, of course, for people who want that. It would be very useful for folks who produce their own electricity. And even then, having a standardized battery pack format can be very beneficial: instead of having a charger specific to one brand/type of EV, it would be a generic one. If you get a new EV, you can re-use the existing charger and battery pack, etc.