Pilot reported an electrical failure and a diversion. Post flight maintenance inspection found the alternator was malfunctioning and needed replacement.

Narrative

I was flying IFR from ZZZ to ZZZ1 on Date at 7;000 ft. MSL via ZZZ when I experienced a voltage drop and alternator failure; I was losing battery voltage rapidly and called ZZZ to report the problem and told them I may lose radio contact and needed to land at nearest field. All electrical power shut down and I lost communication and saw that my oil pressure was at 0 also. The gauges are electronic but I could not take a chance that something more critical was occurring in the engine compartment. The radios came alive for a few more minutes and I was able to contact ZZZ Center and I [received priority] and told them I was going to land at the nearest field. I looked down through the broken layer of broken and scattered clouds and saw ZZZ2 runway below me and told ZZZ I was going to descend and land there. They gave me the Tower frequency. I dialed it in but power went to low and radios went dead again. I have a Garmin GDL 39 that has a back up battery pack attached to the antennae; that shows traffic via the GPS and ADS-B ground stations so I used it to confirm traffic avoidance as I descended VFR. My hand held radio was retrieved and utilized but I did not get a response from ZZZ2 Tower; or I did not hear it due to head phones on.The engine was running smoothly and I made a standard left downwind approach to the field. I lowered the gear manually rocked the wings to insure they were locked in place; I made an uneventful no flaps landing since both are electrically powered. I was met by emergency crew and security when I taxied in to tie down area. Once the plane was secure and it was determined everything safe I was transported to security center; cleared for badging and badged for access to the ZZZ2 grounds. I contacted an A&P who helped diagnose the problem and the necessary alternator replacement over the next few days and flew out to ZZZ1 VFR on Date1 and landed uneventfully there.