Our bikes don't generate until about 2000 RPM, don't charge until about 3500 RPM...These bikes run poorly with a weak battery.
You would need at least a large capacitor to store some power to start, but even then, it would be a hard start....You can test it, remove the battery leads and try to start it....
The system was designed around a battery ignition....ity generally works poorly if at all...
Bikes that can get away with this are bikes with a magneto ignition...not points and coil like ours....
Me? I prefer the electric leg, so I keep the battery for that, plus that it runs so well...