Cardinal 177 pilot reported a complete electrical failure during cruise; requiring a manual gear extension for landing. Pilot believes the electrical demand of a backup artificial horizon may have caused the failure.

Narrative

Aircraft experienced complete electrical failure. Engine was still operating normally. Problem may be the MidContinent Instruments Lifesaver backup artificial horizon. The wiring for this instrument may demand the full electrical load on the aircraft and shuts down everything else. No lights; power; transponder; radios; etc. Lifesaver breaker was pulled but by this time the battery was dead. Was able to contact ZZZ Approach on a handheld radio. [Requested priority handling] because the landing gear had to be pumped down without any green light indication that the gear was locked (again; because of dead battery). Aircraft landed without incident. However; this is the second time that the pilot had an incident with the MidContinent Instruments Lifesaver. This same instrument was checked and had new components and battery installed last year by Company X and failed again. The pilot is an engineering professor and believes that there is something inherently wrong with the instrument's design (not just this one instrument) and that this situation could happen to many people operating aircraft with this instrument.