You won't get much power (Wh, as opposed to mAh) from a cell at a low state of charge. The initial lower voltage of the almost empty cell, combined with the increased voltage sag under load due to the converter pulling increased amounts of current will result in dubious amounts of actual extra energy. In any case, many complicated electronic gadgets already use some kind of voltage regulator that maximizes the runtime of the device, this gadget (if it works as advertised) would be useful only for some direct-drive lights or motors