A power toothbrush, comprising: an elongated housing open at a proximal end, having at least one groove on a proximal portion of each side of the interior of the housing wall; a unitary subassembly inserted into the opening at the proximal end of the elongated housing comprising: a drive mechanism powered by a rechargeable battery; a drive shaft having a distal end arranged to receive a toothbrush brushhead, and a proximal end connected to the drive mechanism within the housing; a control circuit in electrical communication with the battery; a battery chassis for limiting movement of the battery; a housing interlock configured and arranged to hold the components of the unitary subassembly together, the housing interlock having housing interlock tabs; and an end cap having end cap tabs, wherein the housing interlock and the end cap are fixedly engaged together by means of a slot on each end cap tab and a finger on each corresponding housing interlock tab disposed on the housing interlock, the housing interlock tabs and the end cap tabs disposed in resilient contact with the at least one groove in the elongated housing to secure the unitary subassembly in the housing. an elongated housing open at a proximal end, having at least one groove on a proximal portion of each side of the interior of the housing wall; a unitary subassembly inserted into the opening at the proximal end of the elongated housing comprising: a drive mechanism powered by a rechargeable battery; a drive shaft having a distal end arranged to receive a toothbrush brushhead, and a proximal end connected to the drive mechanism within the housing; a control circuit in electrical communication with the battery; a battery chassis for limiting movement of the battery; a housing interlock configured and arranged to hold the components of the unitary subassembly together, the housing interlock having housing interlock tabs; and an end cap having end cap tabs, wherein the housing interlock and the end cap are fixedly engaged together by means of a slot on each end cap tab and a finger on each corresponding housing interlock tab disposed on the housing interlock, the housing interlock tabs and the end cap tabs disposed in resilient contact with the at least one groove in the elongated housing to secure the unitary subassembly in the housing. a drive mechanism powered by a rechargeable battery; a drive shaft having a distal end arranged to receive a toothbrush brushhead, and a proximal end connected to the drive mechanism within the housing; a control circuit in electrical communication with the battery; a battery chassis for limiting movement of the battery; a housing interlock configured and arranged to hold the components of the unitary subassembly together, the housing interlock having housing interlock tabs; and an end cap having end cap tabs, wherein the housing interlock and the end cap are fixedly engaged together by means of a slot on each end cap tab and a finger on each corresponding housing interlock tab disposed on the housing interlock, the housing interlock tabs and the end cap tabs disposed in resilient contact with the at least one groove in the elongated housing to secure the unitary subassembly in the housing.