No - Sharkbanz do not use batteries and thus do not require charging. They are powered by the magnetic field of the earth and are always "on".
As long as your Sharkbanz is not exposed to heat over 160°F (70°C) and the chassis is not physically damaged, then the magnetic technology will not lose its effectiveness. The longevity of the band varies depending on the frequency of use and amount of user abuse. Think of it as a more durable high-quality sport or ocean watch; you're more likely to lose it than for it to break.