Mr. Grace's nurse is showing Mr. Grace how his new stress alarm works. After she's shown him the operation of his lapel unit, she walks over to the filing cabinet and points to a device sitting on top of the cabinet. She tells him, "This is the battery for the spare charger, and it plugs in here," then reaches down and plugs the unit into the wall outlet. Vivienne Johnson messed up her line. To make sense in this context, the line should have been, "This is the charger for the spare battery." Since Mr. Grace is wearing a battery-powered lapel unit, it would make sense for there to be a spare battery, and a charger to charge the batteries.