Among the factors discussed was its ability to "rapidly swap out the Model S battery pack, and the development of specialized public facilities to perform such swapping, which do not currently existbut which we plan to introduce in the near future." (our emphasis)
We've heard this before
Tesla has discussed battery swapping as part of the Model S design at least since 2009. As recently as March, in its previous 10-K filing, it said it was considering implementing some version of the technology during 2013.
The latest information is the statement that "specialized public facilities" for conducting battery swaps are something that it "plan[s] to introduce in the near future". It essentially telegraphs an imminent announcement.
It also eliminates previous discussion of battery swaps occurring at "service centers" in favor of the far more interesting "specialized public facilities."
When asked what this tweet was about, he responded: "Don't forget the mystery announcement. Part 5 of the trilogy"--referring to earlier tweets promising imminent announcements, including the new Financing Plan and Service Plan recently announced.
We still await word on an expansion of the network of SuperCharger quick-charging stations, as well as the "mystery announcement." Both are expected any day now.
Currently, the SuperCharger system offers the fastest charging installed on any electric car. It allows a Model S to add roughly 150 miles in 30 minutes under optimal conditions, and can even complete a full 265-mile "Range" charge of an 85-kWh Model S in a bit more than an hour--allowing owners to take long road trips.
But even SuperCharging is incapable of charging the large Tesla Model S battery pack "faster than you can fill a gas tank."
We are left to believe that the "mystery announcement" is related to the 10-K's battery-swap announcement.
Rapid battery swapping
So what is rapid battery swapping? Just what it sounds like: It replaces a depleted battery pack with a full one, rapidly.
It may be best known among electric-car fans through the struggling Better Place service in Israel.
It would entail driving the Model S into a small automated facility, rather like an automated car wash. A robotic mechanism would remove the battery from under the floor and replace it with a fully charged pack.
Presumably after paying for the service through their touchscreen displays, Model S owners could drive away with fully charged batteries, ready to complete the next segment of their trips.
Musk has previously described this process as equivalent to the Better Place battery-swap process, which can swap out a battery pack in less than a minute.
Unlike Better Place, however, Tesla owners would then pick up their original batteries on the return trip.
There has always been skepticism about whether Tesla would move forward with a battery-swap system, whether for functional or economic reasons.
The company has announced $200 million in capital expenditure for 2013; a major investment in battery-swap infrastructure would clearly require substantial effort and resources.
But the statement in the 10-K and Musk's tweets appear to leave little room for doubt.
And perhaps the need was foreshadowed by Jake Fisher, head of automotive testing at Consumer Reports.
He said of the Model S: "If it could recharge in any gas station in three minutes, this car would score about 110" [out of 100].
Thomas Fisher is a performance-car enthusiast and Tesla Model S fan who lives in Southern California. He works as a business consultant and occasional writer.