Cessna 172 pilot reported an in flight battery failure and electrical failure. The pilot diverted and landed safely.

Narrative

The club safety officer asked me to ferry back a stranded Cessna from ZZZ. I was told it had a dead battery and had since been fixed. Coming from the safety officer I believed him; this was my first mistake. I should have verified the repair myself. Because there was an electrical issue previously I did an extensive pre-flight and I verified the alternator was working on the ground. I checked the alternator by starting the engine and cycling the alternator. Turning off the alternator caused the low volt light to come on so it appeared to be working. The ammeter looked ok as well but this could have been parallax error since I was in the right seat. This was my second mistake. The plane was not equipped with a voltmeter so other than the low volt light; I had no way of monitoring the alternator in flight. The low volt light never did come on in flight. I took off from ZZZ; got flight following on my way to ZZZ1 and was otherwise an uneventful flight. I was cleared into the Bravo via the route. Over ZZZ2 I noticed a data bus failure on the G5 so I took a picture; I figured I would let the owner know once I landed. This picture I took also recorded the low volt light not being on. Quickly after the data bus failure; I looked over and my COM1; a garmin 430; went dark. My com2 and transponder was working however. Since the transponder was working I squawked XX00; continued my course; and tried to figure out what was going on. I tried to raise ATC on com2 but I wasn't able to get it to work. I cycled the alternator off; and the G5 reported external power lost so I turned it back on. Then my com2 went out; so at this point I knew I had a more serious problem. I squawked XY00 while the transponder was still working. I looked up the [priority handling] checklist from the POH. It advised me to turn off the alternator but that didn't make sense because it only made the problem worse. At this point I figured the best thing to do was get on the ground ASAP as the aircraft was failing. I saw ZZZ3 to my right so I turned for the airport and started descending. While I was descending towards ZZZ3 I tried to call ZZZ Approach on my cell phone but I couldn't get it to work; I was probably too high still. I had a handheld but with the rapid descent and trying to use my cell phone; I was too busy and didn't even think about using it; another mistake. I circled over ZZZ3 and after a circle or two I saw a green light gun from the tower. I wagged my wings to acknowledge and proceeded to enter a left downwind for runway XX. I forgot to run my pre-landing checklists; I tried to extend the flaps; I was able to get 10 degrees but no more. I focused on landing and landed safely and exited the runway and stopped. I was going to try my cell phone again but then I saw a flashing green light from the tower. I luckily had my light gun signal cheat sheet on my kneeboard so I knew I was cleared to taxi. I taxied towards the FBO. I had one runway to cross on my way so I stopped at the hold short bars; looked at the tower again and verified I was still getting a green flashing light; so I crossed the runway and headed to the FBO. Once I shut down the airport manager met me and we chatted all was good. I called ZZZ Approach on my cell phone and let them know I was ok. Ultimately I did most things right; I wish I remembered to try my handheld and ran more checklists. I should have verified more information on the maintenance status on the plane; I had verified the 100hr; annual; and ADs were current but I should have inquired more as to why the plane was stranded. I also should have monitored the electrical system more in flight but I'm not sure what that would have done as my photo verified there was no low voltage light.