That is some interesting suggestions. Curious have you done this with succuss. The 4th gear running part down street.
Dude..never bump started a bike before?
May or may not work on a modern FI bike as the electronics will need some power to actually be awake enough to inject fuel. If the battery is flat to the point where there's not even enough left to run the ECM, it may not start.
Oldschool carb, well, always a viable solution...although bump starting a big CC V-Twin is a whole different ball of wax due to their compression ratios, but that's a different story.
battery tender worked -- bike is back to starting
now, do I charge the battery every time I don't use the bike?? How long will this last for?
In the winter months the battery can (and should) be always left on the tender to make sure it stays at 100% SOC. Lead acid batteries self discharge when left sitting, and many bikes also have parasitic draws that can speed up discharge as well.
Just make sure you use a proper TENDER, and not a "trickle charger". The latter will cook your battery if left on.
Now, as for your existing battery, having been flattened and possibly left that way for some time, it may have been damaged and now only carrying a surface charge - enough to start the bike after being freshly unplugged from the tender, but maybe not enough to start the bike again after it's been sitting having lunch somewhere for an hour or two. The only way to tell for sure will be to have it load tested and see if it performs properly.