This is actually just the latest step in a series of batteries called bio-batteries. They can run off of a number of bodily fluids, like sweat, urine or -- ah, there it is -- tears. So they can get power from all of the bodily fluids humans release in response to extreme terror. It's really a fear-powered battery, we guess. Hey, Monsters, Inc. was real!
Oh, also, it has to be implanted under the skin to work.
Even if it looks like a hunk of charred skin from a hot dog, it's actually an amazingly advanced little device. It has the texture of paper, but it draws electrolytes from your fluids and channels them through nanotech carbon tubes to create a usable energy supply.
Still, it's cooler than the alternative, which uses blood-feeding yeast.
The goal is not, apparently, to make a huge one and power it with a lake of blood from conquered human victims, but rather to help power medical implants. The papery nature of the batteries means they could be printed in sheets and easily cut to the size and shape needed for the patient. Then, once the thing is drawing juice from your natural fluids, you don't have to worry about changing the battery. It also seems like you could replace the mat in a UFC ring with this stuff and power the whole stadium with the sweat and blood from fighters, but we haven't heard of any prototypes for that yet.
Apparently broken teeth short circuit the whole thing.