PA-34 Seneca pilot reported electrical failure inflight prompting an immediate landing the nearest suitable airport.

Narrative

I filed an IFR flight plan back to ZZZ. I departed with my clearance. About half way to ZZZZZ; my first fix; the plane suffered a complete electrical failure. I quickly checked what I could; but could not regain power to my electronic Flight instruments or radios. I had suffered a complete electrical failure. I turned back and started to descend to 3;000 [ft] to try to pick up the shoreline because I was in instrument meteorological conditions (IMC) and did not want to continue over the lake in those conditions. I also brought up ZZZ1 on my iPad with ForeFlight and proceeded to fly towards ZZZ1. I also activated my emergency locator transmitter (ELT). ZZZ2 contacted my wife to try and find out where I was because I had activated the ELT. She called me and when I answered; I asked her to call ZZZ2 back and tell them I'd be landing at ZZZ1 [with] No Radio (NORDO). I soon got down to 2;000 feet and entered the pattern for XR and landed. After landing; I taxied to [the FBO]. The plane was towed across the field to [maintenance] and within a few days they checked it out. During the inspection they found a battery cable had come off the battery. Their Airframe Log Entry sticker says the following:'Re-secured negative battery cable [and] Re-set landing gear emergency extension handle and performed gear swing. This aircraft was repaired in accordance with the manufacturer's maintenance manual. All systems interrupted have been tested and/or leak detected as necessary. This aircraft is airworthy and is approved for return to service with respect to the work performed.'I picked up the plane and flew back to ZZZ on an IFR flight plan. All is working as it should.