C172 pilot reported loss of all electrical power during cruise and continued to land at destination airport where ATC used light gun signals for landing clearance.

Narrative

The problem arose when i was 10 miles out of my departure airport; when sunset began. i noticed my battery voltage was showing below 12 volts. it was reading 11.8 volts. i decided to monitor the rate at which voltage was going down before making a decision on what to do. After a couple minutes i contacted ZZZ Approach Center and notified them that i was running on a negative battery charge. I was on their radar with VFR flight following into ZZZ airport class D airspace where the airplane is stored. ATC asked me what my final destination was and if this was [an] emergency. I told them I was not declaring [an] emergency because after evaluating the decrease in volts; i decided i would be able to make it to my destination using minimum electrical equipment. I made this request to use minimum equipment to ATC; they said that was okay and to monitor frequency whenever i could. ATC also told me to descend maintain at or above 4;500 feet when i was East of ZZZ1 airport and continue direct to my destination. I told ATC okay; i will monitor frequency and let you know if i need any assistance. I also told ATC that if they didn't hear back from me that meant i lost all battery power. ATC said okay. so i turned off my radios and all other avionic equipment that was not necessary for my flight to conserve battery power. I have portable ADS-B in on my Stratus that connects to my foreflight on iPad so i could monitor any traffic in my area. When i was East of ZZZ1 i tried turning back on my avionics to monitor the radio frequency; and when i tried calling ATC i heard nothing back from them; i tried this four times before squawking 7600 on my transponder. I was only able to keep my transponder squawking 7600 for 2 minutes before i lost all electrical power. I had no lights; no radios; and no flaps. I decided to continue to complete my flight and land at my destination airport; assuming that ZZZ Approach would notify the Tower at my destination airport that i had lost all electrical equipment i would look for the light gun signal that i was cleared to land. My backup plan was to use my portable radio or call the Tower from my phone if i saw no light gun signal. When was 2 miles out from ZZZ airport i saw the green light gun signals meaning i was cleared to land. So i entered right downwind in the traffic pattern for Runway XX R. I landed safely with no damage to me or the airplane. When i exited the runway for the taxi way i looked for my next light gun signal that i was cleared to entry the next taxiway; i saw the signal and proceeded to my hangar. after doing a post flight inspection i contacted the Tower from my phone and notified them i landed safely and the airplane had no damage; they asked me what happened and i told them i lost battery power. The Tower said they could not see my airplane because i had no navigation lights or landing lights. I asked them if there was anything they needed from me and they said no just happy i landed safe.