Keeping Seldom Used Motorbike Functional?

How long can it sit before the battery won't start it?
If it's just a couple of days, the battery is shot. Replace it.
If it's a couple of weeks, battery is so-so, keep on battery trickle charger.

If it's 5+ weeks, probably good, but charge on trickle charger once a week or put on smart charger that will stop charging when battery is full.

Live on a hill and "push-start" it.

Yes I agree trickle charge and gas additive  for storage if they sell it in Vn

We are going to test this theory.  I just put a new battery into my Triumph Tiger 800XC in the summer of 2019.  Since I haven't been able to go home at all this year it's been on a battery tender for more than a year already now, soon to be 24 months by the time I get home in June 2021.

I'm leaving my bike here in Malaysia for God knows how long...no idea when I can return. Would it make sense to simply unplug the battery before I leave?

Drain  the carburetor of all fuel
Un hook battery cable to bike

Hooked wrote:

Drain  the carburetor of all fuel
Un hook battery cable to bike

If the bike is going to sit for more than a month, I would completely drain all the fuel, fuel left in a bike goes stale quickly & causes all sorts of problems!