I have a gravely 152 pro and when I charge the battery it starts and run for a little while, also, sometime when I engage the blades it shuts off. I replace the gas filter, put new gas into the tanks, change carburetor.
Are you running the throttle up to full speed before you engage the blade PTO? I was told to do so when I bought mine, and I notice when I engage the PTO, it does put a strain on the engine and it revs down quite a bit. I'm guessing if the throttle isn't fully open, it could strain the engine enough to shut it down.