Possible voltage regulator issue?

First some history. My rudder was damaged by a tornado. Being my plane is an E-AB which I didn't build I had to get someone to build a new one. As a result the plane sat for 4 months at the mechanic's shop. This past weekend we installed the new rudder and I had a chance to start the plane up. It has a Rotax 912 ULS. My mechanic checked and topped off the battery. It was mid to upper 50's and considering it had been sitting so long it started up pretty easy. Everything looked good. It was too windy for a flight test so I taxied back to my parking spot and just ran the engine for about 10 minutes till all the temps came up to normal. As an FYI with no load on the system I was getting about 15.3 volts when I ran the engine up to 4000 RPM. The next morning I intended to do a test flight. It was mid to low 40's. Normally it's a little hard to start but it just wasn't having it. Basically I killed the battery so I used a booster(something I've done in the past)and jumped it. Started and all seemed good. Run up OK. For testing purposes I just did a flight in the pattern. I taxi back for another go and I see my transponder is off. I boot it back up but it goes out again. Further attempts were unsuccessful. I cycle the avionics switch and try again. No luck with the transponder and now the radio is acting up. I cycle the avionics again and now radio is OK. I'm showing about 8 volts, normally with a load(strobes, taxi lights, standby fuel pump) and engine at idle It's just just below 10. I guess because I'm dumb, I did a couple more trips in the pattern. Rudder working fine. I taxi back to my parking spot. With the engine off both radio and transponder are fine. With everything else turned off I try restarting the engine and all I'm getting is a clicking noise. I'm thinking that the battery didn't charge and the other symptoms are very similar to the time 3 years ago when my voltage regular stopped playing nice. Any suggestions what else I should check? I plan on checking the battery voltage and charge it as needed. Check/clean the connections and see if anything works better.