Because the batteries wouldn't have to be tested while you wait. Like laptop batteries, they could have their own embedded controllers that would keep track of each individual unit's charge state and condition. (Actually it's almost certain that they already do.)
The analogy I like to use is swapping out propane cylinders for a gas grill. It should take less time to refuel an EV than a gasoline-powered vehicle, not more.
This is also important for power management, if Musk's prediction comes true and half of all cars sold by 2025 are indeed electric. Swappable batteries can be charged when/where the power is available, using industrial rates and infrastructure. Instead of seeing gasoline tankers driving around, you would see trucks delivering and picking up batteries from service stations.
People will understand why hardwired batteries are a bad idea as soon as half their neighborhood tries to charge their EVs every night the way we currently charge our smartphones.
I don't really like the idea of battery swapping. It seems like a big hassle. The current Supercharger seems totally fine. I guess it remains to be seen how well it works in practice, once a lot of people have the cars, but right now things look really good.
One of the most common pieces of anti-EV rhetoric is "the infrastructure doesn't exist". This is actually FUD. The infrastructure is everywhere: we have electricity pretty much everywhere. (Consider: all these gas stations have electricity, so the penetration of electricity is a superset of the penetration of gasoline). What we don't often have is the right plug, but that is a relatively small problem.
But if you start talking about installing a widespread battery swapping paradigm, then that is a huge infrastructure problem, because you need to have stocks of all these physical things all over the place.
On the other hand, with Supercharger, you don't need that. You just need some electricity. It is much simpler.
If you wave your hand enough anything is trivial. The "some" you are talking about is 250A @ 400V (100kW) which is a trifle more than a typical gas station can readily supply (especially if you want to charge more than one at a time).
Besides, do you know that a typical gas station can't readily supply 100kW? How do you know? Has anyone even thought about this seriously (except Tesla)?
I am a little bit shocked by the amount of specious naysaying that is happening in this thread. This is supposed to be Hacker News, where people are motivated to really think about problems, to build solutions, etc, etc. I don't see any of that attitude in some of these replies.
Right now, peak electricity usage times are during the day. This is why in most urban areas electricity is cheaper at night: they want to encourage you to distribute your usage more evenly throughout the day.
The NEMA 14-50 (a.k.a. standard appliance outlet that most people plug their dryers into) is a totally fine plug for an EV. It will charge the car up fully overnight. This plug is going to deliver you, at maximum, 40 amps at 220 volts.
Electric dryers often use something like 25 amps at 220 volts (of course it varies by machine). This is not far from the 40 amps we are talking about. So this whole "grid can't handle it" pseudo-panic is sort of like worrying that everyone is going to run their dryer at the same time, times 1.5, at off-peak hours. It is just not a big deal. FUD.
Your local neighborhood transformer might be serving only 5 houses. If one or two of them decide to charge an EV every night, the transformer may not get a chance to ever cool down, like it is designed to do.
Re: 220V outlets, it's surprisingly hard to find the true average power consumption by a dryer, now that I just tried. I do know that the heating element in a dryer is usually rated for 5000 watts+, but you have to keep in mind that it doesn't run at a 100% duty cycle, even on high heat. (I can't find anything that talks about what the typical duty cycle on high heat is, so maybe I'll measure mine the next time I dry something.) I'm pretty sure it would more or less nuke your clothes if the dryer dissipated over 5000 watts all the time.
Point being, if an EV charger really does draw 40 amps at 220 volts, that is about twice the real power consumption of a clothes dryer. This is a non-trivial amount of juice. It would be a massive problem if half the automobile-owning households in the US started charging their cars all night long at those rates.
It's not just a matter of you not personally having any use for swappable batteries. It's a matter of electricity not being quite as trivial to generate and distribute as you suggest.
Nobody that I'm aware of, including me, is trying to spread FUD. I would gay-marry Elon Musk, if I were gay. I wish him all the success in the world. But the numbers behind his prediction simply do not work... unless he has something up his sleeve along the lines of the Better Place concept.
40 amps at 200v will completely charge a Roadster in something like 7 hours. I don't know how long for a Model S, but it is probably longer. I am only familiar with the day-in, day-out of the Roadster so I will stick to that mostly.
So the "charge the car all night (7-8 hours) scenario" only makes sense if you need to charge up the battery 100%, i.e. you were on fumes before you plugged it in, which means you drove 200-240 miles the day before. This may be true for some people but it is not going to be true for most people most of the time.
I drive from SF to Berkeley and back most work days, a 25-minute commute each way, and I like to drive it like a sports car, so I use relatively a lot of power for that length of trip. Generally I use about 20% of the Roadster's battery on such a day, so that's probably about 1.5 hours to charge in a 220V outlet. If everyone did that, you would probably want to stagger the charging times, but it is totally doable even with current setups.
I do think that there would be some increased power draw and that we would want to beef up our electricity infrastructure a little. But that is pretty different than what I see as a Republican talking point, which is something like "there is no way that the USA can support everyone plugging in their EV, it's impossible." That is not my experience as an EV driver.
When I was coming up with the dryer analogy I was just using numbers I pulled off the Internet about what people were measuring their dryer's pull at. It's possible dryers just are not very efficient, I don't know! (Though I thought the whole Energy Star thing was supposed to put pressure on that).
According to a 2011 study conducted at Lawrence Berkeley National Laboratory and the University of California Berkeley, the currently estimated reserve base of lithium should not be a limiting factor for large-scale battery production for electric vehicles, as the study estimated that on the order of 1 billion 40 kWh Li-based batteries could be built with current reserves. Another 2011 study by researchers from the University of Michigan and Ford Motor Company found that there are sufficient lithium resources to support global demand until 2100, including the lithium required for the potential widespread use of hybrid electric, plug-in hybrid electric and battery electric vehicles. The study estimated global lithium reserves at 39 million tons, and total demand for lithium during the 90-year period analyzed at 12–20 million tons, depending on the scenarios regarding economic growth and recycling rates.
If we use those figures, 39 million tonnes / 1 billion cars comes down to 39kg per car; not too far off. According to this , there were around 60 million cars produced in 2011. Conservatively assuming that that grows to 100 million in 2025, that's 50 million electric cars per year according to Musks prediction. At 39kg per car that is around 2 million tonnes of lithium per year. Not too far off my 2.5 million tonnes. So my point still stands that we have to increase lithium production around 70x just for cars (and consider trucks, cargo ships, motorcycles, farming vehicles etc). Perhaps we will be able to do that without increasing prices significantly, perhaps not.