78 KZ200 quit on me

While riding my 78 KZ200 today it quit on me. When I tried to start it the electric starter did nothing. I was able to kick start it and get it home. While going home the signal lights quit working. As I pulled into my driveway it quit again and I was unable to restart it. I got it in the garage and nothing worked. After an hour or so the lights were dim, the signal lights were slow, and the electric starter offered. After another hour the lights were stronger and I was able to electrically start it. While running I put a meter across the battery and it read 10 volts. When I turned on the lights it dropped to 9 volts and revving the engine did not help. The battery is brand new. Is this a problem with the voltage regulator or something else?

This is my first post. I just picked up the bike from my dad. It's been sitting for a while. It's a 78 with just over 7,00 miles.

Thanks in advance for your help, Jim