A lithium rechargeable battery includes an electrode assembly having a first electrode, a second electrode, and a separator interposed between them, a can having an opening to contain the electrode assembly, and a cap plate coupled to the top of the can. The tunable resonator is a MEMs tunable resonator wherein the tuner is affected by moving a moveable mass, associated with the resonating portion of the resonator, form a first position to a second position such that the moveable mass is held in the first position or second position by a detent rather than a constant electromagnet magnetic or electrostatic force applied thereon. The first plate has a curved portion with a height higher than that of the folded-back piece and disposed adjacent to an outer peripheral edge of the folded-back piece.