interesting article. though my shenanigans detector is starting to beep when I get to the "they broke into my office" part.
Either way though, the concept is somewhat sound. From an electrical engineering standpoint there are questions that need to be answered first though. Right off the block I have to ask how it can do anything at all without drawing power from the battery in the first place. Even if the battery is "full charge" and it's not having to boost anything, it has to operate the FET that is strapping the battery to the device. That and the monitoring electronics, while in "passive mode" have to draw something. I could see this as a slow-discharge problem.
Second, you can't step up (or down) DC power for free. DC step-up is somewhat notorious for being inefficient. Here again I see energy loss due to heat in the electronics.
Third, stepping up or down requires an LC circuit. Both the L (inductor) and the C (capacitor) tend to be the largest two parts in the arrangement. (the stepping IC being the third) I'm really amazed they found space to fit those into the sides of that widget. Unfortunately, to cut corners on size with L and C, you lower L and C, and that lowers efficiency. Again losing power.
Fourth, even under the best of conditions, steppers waste power and generate heat. I used a 12->5 step-down in my truck to run my USB devices, and it overheated and smoked on me, it had gotten quite hot before it failed. And this was a larger, manufactured unit, not some supermini hack. That heat directly reflects energy lost from the source. And when your source is a battery, there is just that fixed amount of stored energy to work with, draining that directly affects runtime.
All of the above bite into total available energy. The question then becomes "is it a winning proposition? Can you get more time out of your gear with the gadget than without?" In other words, yes, it probably can drain a battery more completely, but are you really getting to use any of that in a net gain in total usable power? I wouldn't mind having one to play with, but I would start my testing with some skepticism.
A fourth, less related issue is the size. It looks like they did a good job of keeping the top and bottom contacts very thin, but I've seen several gadgets that require the cells to be round to use them, like my digital camera whose batteries slide in vertically into cylindrical holes. This wouldn't be physically compatible.
