Last week, Tesla started selling used cars. It made the move quietly, while we were all thinking about the company's new batteries for home energy storage.

The pre-owned Model S sedans come from owners who have traded them in—mostly to upgrade to the dual-motor P85D. They are available for sale in 11 markets, including New York, Los Angeles, Washington, D.C., Florida, and the Bay Area (of course). Before you ask, you don't get a new battery. You do, however, get a four-year, 50,000-mile limited warranty, plus the remainder of the original eight-year, infinite mile warranty that covers the battery and drive unit. So if the lithium-ion pack under your feet craps out, you'll probably be covered.

The pre-owned Model S sedans listed online aren't cheap, but they are available. And that may be their biggest selling point.

The most affordable ones are $65,000, and some cost more than $100,000. That's not far below the price range of a new Model S. Tesla says it sets the price based mostly on how much it had to pay the original owner for the trade-in. Its residual value guarantee program promises a Model S will still be worth at least 50 percent of its base price, plus 43 percent of the cost of options (including an upgrade to a more powerful battery pack).

Even without that explainer, Tesla could justify high prices. These cars haven't changed much since they were first delivered. Most of them have pretty low mileage (lots have fewer than 4,000 miles). Electric vehicles don't have many moving parts that need replacing, especially compared to a car with an internal combustion engine. There are fewer fluids to swap out, there's no exhaust system. The brakes don't get worn down so much, thanks to regenerative braking.

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Plus, the Model S has only been available for three years, so there hasn't been enough time for serious depreciation. The biggest question mark is how long the battery will last—and the car's so new, we don't really know yet—but the very generous warranty makes it a moot point. With that guarantee, you've basically got a new car.

Another contributor to the high cost is the lack of the juicy subsidies that knock thousands of dollars of the price tag of a new EV, like the $7,500 federal tax credit and the $2,500 rebate you can nab in California. Owners cashed those in when they picked up the cars new, so when you buy or lease an old Model S, the government's not going to help you out.

Lastly, there's the fact that Tesla is still selling cars as fast as it can build them. Demand is greater than supply, so the upstart automaker can demand a premium for any of its cars. Waiting time varies by model and time of year, but order a new Model S now, according to the company's website, and you'll be waiting for delivery until late June. Reserve a Model X SUV, due to hit the market in July, and you won't get behind the wheel until 2016.

All of which means the pre-owned program is more about making Tesla cars available than making them affordable. This is, after all, an in-demand luxury car, and one of the most serious complaints about it is that it's hard to get one (also: no cup holders in the back seat). "It's just another source for Tesla buyers who want one and couldn't get on the listteor didn't want to wait for the new ones that are back ordered," says Karl Brauer, a senior analyst at Kelley Blue Book.

Tesla says "the Pre-Owned Model S program gives even more people the opportunity to own Model S, and showcases its value." That second part is important. A secondary market, Brauer says, can "help validate the car's lifecycle," and prove it's more than "a shiny new vehicle that's interesting."

The timing of the used car program is logical. Last October's introduction of the Model S "D" variants, with a second motor and all-wheel drive, encouraged customers who want the latest and greatest to trade in their suddenly lame single-motor, rear-wheel drive cars. Tesla has been offering a three-year lease since early 2013, so those cars will be coming back soon. And the much anticipated Model X will trigger more Model S trade-ins.

What we don't know yet is how many people will want an older Model S when they could spend a bit more money for a dual-motor "D" version, or the Model X. But if Tesla's cars continue to generate the demand they always have, that shouldn't be an issue. And if they don't, there's always that home energy scheme.