A single common load is provided for both space heating of the interior of an enclosure and for testing of a back-up battery therewith. The common load is coupled to either the battery for momentary load testing thereof, or to a power supply when heat is to be generated by the load for space heating of an interior of an enclosure. Providing only a single load for both space heating and battery testing results in reduced component costs, space savings and simplification of connections and wiring harnesses required. Power resistors, active components such as transistors or MOSFETs, and/or resistive heat tracing may be used as the common load, and deposed within the interior of the enclosure.