Most TVs' USB ports don't have a strong enough output to run the 4K Fire TV, which needs 1200mA to run continuously, so you can't use an ordinary cable. Plugging the device directly into a TV's port leads to resets -- sometimes, it doesn't even work. Mission's has a small box with a lithium-ion battery that stores excess current, and it releases that extra power when the Fire TV needs more electricity than what the USB source can provide. The solution is now available on Amazon for $20, but it's currently on sale for $15 at Mission's website if you're just purchasing to sate your curiosity and want to save a few bucks.