Ni-MH battery packs are reliable and steady against external conditions. They have the long life - can make 1000-1500 charge-discharge cycles (3-5 years). Are well stored during long time. Usual defect is "the effect of memory" as a result of which the accumulator gradually forgets a part of capacity. The capacity can be restored, but it is almost impossible in home conditions.

Ni-MH battery pack will work long in not loaded mode of calling. And at an opportunity of periodic restoration, "the effect of memory" will be under control.