An instructor pilot reported electrical failure in a C172 and continued to the destination.

Narrative

Hello. Night flight with my student to ZZZ1 from ZZZ. He's working on his private. Squawk sheet did note low volts 24 volts. Should read at least 25 volts during pre flight. I did not notice that during the pre flight. We made it to ZZZ1 and we shut engine down at the flight school at ZZZ1. We did another pre flight and everything seemed fine; I did not specifically check the volts during that preflight myself. We made it back over to ZZZ VOR; roughly at ZZZ2 we noticed lots of flickering of coms and navs and a noticeably dimmer instrument lights as well.Really soon after that we squawked 7600 as the comms failed; my student went on the mic and requested priority handling. The person who responded after his request was a person saying this is guard. We were still on a self announcing frequency XXX.XX. We did not switch frequencies after that because all comms went dark. The transponder died as well as all electrical. Once we got over the pass we saw the steady green light from ZZZ tower. I did try to call ZZZ tower but I had the number saved from chart supplement. I now have the actual tower number saved in my phone. We landed at ZZZ and were escorted by fire trucks and airport operations.Airport operations asked what happened and how much fuel was on board; they took some notes and told them total electrical failure. They left minutes after that.