Tesla's cars are technologically impressive.They're very fast, they can all but drive themselves, they can be summoned from a garage with no one at the wheel, and they are routinely improved by software updates over-the-air that allow owners to go to sleep and wake up with a new car in the driveway.Everyone in the auto industry now grudgingly admits that Tesla has forever altered consumers' expectations for how advanced in-car tech should be.But Tesla's most advanced feature is largely hidden — and will need to undergo a big change in the coming years if the electric-car maker hopes to realize the far-reaching vision of CEO Elon Musk.It's the batteries, stupidThe secret sauce at the core of Tesla's disruption of the traditional car business is its unique battery design and the powertrain software than manages how the electricity is delivered to the vehicles' electric motors .

And, as an aside, scorching performance the Model S P90D with "Ludicrous Mode" is as fast as Ferrari, Lamborghini, and Porsche supercars .But that range comes at a price.

What this means is that Teslas need enough power to move themselves around before they can even think about range or acceleration.Lithium-ion batteries also rely on ... lithium, which is a limited, costly resource that is currently in wide demand not just for electric cars, but also for pretty much all the rechargeable consumer electronic gadgets on Earth.This is why Tesla is building a massive battery factory with Panasonic in Nevada; if the automaker is going to deliver 500,000 cars annually by 2018, it's going to need something on the order of 4 billion individual Li-ion cells every single year.The core problem here isn't actually that daunting number — it's the power threshold that Li-ion is now approaching, in terms of battery chemistry.

Simply put, the chemistry of Li-ion can't ultimately provide the range that a very fuel-efficient all-gas-powered or hybrid gas-electric vehicle can.The solution is to add more cells, something that Tesla has done since it was founded, but that's a slippery slope.

The only byproduct is water, the vehicles use electric motors and could presumably have Tesla-like performance , and the fueling infrastructure is already in place; they're called "gas stations.

But that may be exactly what it's up against by 2020.NOW WATCH: Here s Tesla s massive plan to meet the demand for 375,000 Model 3 preordersLoading video...

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