If you want to idle stationary, remove the headlight fuse while doing so. (and fan the air cooled motor) That should relieve the alternator load enough so the battery can charge at very low RPMs. When the charging system was originally introduced, the bike had a headlight switch. This was before govs mandated headlight on all the time for MCs. Newer Honda models still had the same alternator design.
With full electrical load, the battery doesn't charge much if at all, since the alternator makes about 1/3 of full potential at idle RPM.
Also, don't ride it like a Harley. These engines thrive on RPM. Lugging them at low RPM isn't doing them any favors.
You can find the "breakpoint" for battery charging on your particular bike, by attaching a voltmeter to the battery terminals and watching for voltage trend with RPM. Battery will slowly raise the battery voltage when the alternator RPM spins fast enough to power both bike and have enough extra to charge battery.
Cheers,