The two unavoidable truths of your phone are that you've got to carry it and you've got to charge it, so why not unite those concepts in blissful matrimony? Case-Mate's new Fuel line of holsters have batteries on board that can keep your phone charged simply by snapping it in place as you would with any other belt-clip holder, so it's a nice value-add without much downside -- and there's a power toggle on the Fuel to prevent it from doing it's thing if you want to save the juice for later. Models are available for the BlackBerry Bold and iPhone 3G currently, providing up to a claimed 7 or 9 extra hours of talk time, respectively. They're $80 a pop, but then again, that's no more than a Mophie Juice Pack Air
-- so if you need insane stamina, pick your poison.