this looks to me like a variation of nickel iron hydride cell, hydrogen is stored within the hydride but can give off a voltage potential, when used up you simply recharge, if however the batteries innards were exposed to air the hydrogen would dissipate and the battery would become useless.
there are many different batteries using the same technology, on the site it also says it uses the same technology as hybrid cars, someone correct me if im wrong but dont hybrids use Lithium Ion cells