http://www.tantronics.co.uk/acatalog/Info_1!chg-gp-pbusb-18.html Only an example. You can get 2 cell ones and sets with higher capacity batteries (2700mA) for the same price or less than one of those USB cells. The only advantage of these USB cells is if you only wear speedos outside, as the inner pocket of speedos has very limited capacity and weird bulges might get you noticed ;)