An assembly of components for modifying a battery compartment to allow the use of batteries of a size other than originally designed. The assembly includes a hollow, electrically conductive, cylindrical adaptor, a first end of which is internally threaded for attachment to the existing battery compartment and a second end of which is externally threaded for acceptance of the existing battery compartment cap. The assembly further includes a hollow, electrically insulative, cylindrical insert. The adaptor and insert each include conductive electrical elements to connect a new configuration battery positioned within the insert to the existing battery compartment and compartment cap contacts. The adaptor and insert are coaxially aligned and loosely attached together in a manner that allows free rotational movement between them about a common central axis while retaining the adaptor and insert in close association.