We replaced the battery of a Suzuki GSX-R1000 one time for a Lithium battery and saved over 2 kilogram on total weight, see article Lithium Motorcycle Batteries - Save more than 2 kilogram.
The downside of a Lithium battery is that you cannot use the standard charging system, it needs to be modified. Also the average charger for in the garage can also not be used with a lithium battery.
I have seen some special lithium motorcycle batteries that have a on-board electronic conversion circuit so you can use it as a regular battery. The negative thing about this batteries are that they are pretty expensive.
I have no idea who is selling lithium motorcycle batteries in Thailand, but you can import them from Japan without any import duty (make sure it's a “Made in Japan” product).
As you scooter is a Yamaha Nouvo SX I doubt that anybody has a standard conversion kit available. I would recommend that you reconsider and look for a good quality regular maintenance free battery. If you would like to read a bit more about motorcycle batteries you can take a look at New Motorcycle Battery – But what to look for?.
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Lithium Motorcycle Battery
