You may have seen The Batteriser in the news recently. Our friend Dave Jones takes a look at their claims and demonstrates why their claims are total junk. In their patent they use lots of generalization that are not true in reality. A good electronic designer will design a battery powered device to operate to a voltage much lower then they are stating. Dave had a ton of battery powered devices around the lab and guess what, none of them dropped out at the claimed typical cut off voltages.
The one thing that I can say that I really like is the very small design of the design, obviously they are slapping their boost convertor onto an existing AA battery so the battery holder must be able to accept the battery with the device attached.