Cub Cadet Zeri Turn

I have a 2020 Cub Cadet with a 22hp Kawasaki engine which I have owned since new. Last year, it started to discharge the battery while it was running. I replaced the battery, then the voltage regulator and most recently the alternator. but the problem still persists. If I charge the battery, I can run the machine indefinitely, but if I run it for about 1 1/2, it will not restart without recharging the battery. I run the mower at full speed. Any one got any suggestion as to what is causing the battery not keeping its charge?

With the engine running full speed, what is the voltage at the battery. Should be 13.5-14.5 on most engines. Also is the regulator properly grounded. Won't work if the regulator case isn't grounded. Also make sure you are getting battery voltage to the regulator.