A rotatable adjustment knob (10, 10') configured to provide a user-selected input to an optical or electronic device (34, 34') having a battery-powered component and an annular mounting channel, the channel defining a seat having a surface at a bottom of the channel and an outer circumferential sidewall bordering the surface, the rotatable adjustment knob (10, 10') comprising: a knob body (30, 30') mountable to the device for rotation about an axis (36, 36') extending outwardly from the device so that a degree of rotation corresponds to the user-selected input, the knob body including a bottom face, an upper cylindrical sidewall section defining a graspable neck section, a lower cylindrical sidewall section defining an outer channel section, and an opening into a battery compartment (14, 14') sized to receive a battery, characterized by the knob body (10, 10'), when mounted to the device (34, 34'), having: the bottom face configured to confront and turn relative to the surface of the seat, the graspable neck section extending away from the channel and sized to be grasped and rotated relative to the outer circumferential sidewall, and the outer channel section extending within the channel and sided to confront the outer circumferential sidewall; electrical contacts (240, 290) housed within the battery compartment (14, 14') and providing a battery connection for the battery-powered component; a lid (12, 12') pivotably attached to the knob body for movement between a closed position in which the lid covers the opening, and an open position in which the lid is pivoted away from the knob body and the opening to facilitate access of the battery compartment, the lid remaining attached to the knob body while in both the open and closed positions for rotation with the knob body about the axis; a resilient seal bordering the opening and confronting the knob body and the lid while the lid is in the closed position; and a latch to releasably retain the lid in the closed position. a knob body (30, 30') mountable to the device for rotation about an axis (36, 36') extending outwardly from the device so that a degree of rotation corresponds to the user-selected input, the knob body including a bottom face, an upper cylindrical sidewall section defining a graspable neck section, a lower cylindrical sidewall section defining an outer channel section, and an opening into a battery compartment (14, 14') sized to receive a battery, characterized by the knob body (10, 10'), when mounted to the device (34, 34'), having: the bottom face configured to confront and turn relative to the surface of the seat, the graspable neck section extending away from the channel and sized to be grasped and rotated relative to the outer circumferential sidewall, and the outer channel section extending within the channel and sided to confront the outer circumferential sidewall; the bottom face configured to confront and turn relative to the surface of the seat, the graspable neck section extending away from the channel and sized to be grasped and rotated relative to the outer circumferential sidewall, and the outer channel section extending within the channel and sided to confront the outer circumferential sidewall; electrical contacts (240, 290) housed within the battery compartment (14, 14') and providing a battery connection for the battery-powered component; a lid (12, 12') pivotably attached to the knob body for movement between a closed position in which the lid covers the opening, and an open position in which the lid is pivoted away from the knob body and the opening to facilitate access of the battery compartment, the lid remaining attached to the knob body while in both the open and closed positions for rotation with the knob body about the axis; a resilient seal bordering the opening and confronting the knob body and the lid while the lid is in the closed position; and a latch to releasably retain the lid in the closed position.