I once had the battery fail on an AfricaTwin in north Thailand, cant understand how, but one of the terminals came loose on the inside, so it was gone. I went to a scooter shop and they managed to get a replacement which wasnt the same as original.. im 90% sure that it was 12V 9Ah, it was a for a scooter anyway. Sorry I cant be positively sure about this, as its been a few years, but that replacement worked perfectly well for my return to Bangkok.
BTW, may I ask about your shipping from indonesia to calcutta.. im planning to go from India to Thailand later this year, and trying to find out about the shipping options (possibly to Malaysia or Indonesia, too). What company did you use, how long it took you, any big trouble with paperwork, etc.. and I assume you flew yourself, right? Any info on that would be much appreciated as well! Pekka