Replacing the battery of your motorcycle, it sounds easy enough. When a battery won't take or hold a charge it's time to go shopping for a replacement battery. If your motorcycle came from the factory with a VRLA (maintenance-free) battery, don't try to save a few Baht by replacing it with a conventional battery. If you insist on saving money, buy a VRLA motorcycle battery with an acid pack and activate it yourself.
However, if you ride a modern motorcycle, buy a factory-activated battery: some motorcycles have their batteries mounted at angles that may pose some risk of leakage with customer-activated motorcycle batteries. Some motorcycles have their batteries mounted upright and can use customer-activated batteries (still I would not recommend the use).
Owners of older motorcycle can maybe not take the advantage of the newer battery technology. The problem is that VRLA batteries have more stringent charging requirements. Older motorcycles may have charging systems that supply either too much or too little voltage. You best contact the manufacturer, dealer, or post your motorcycle make, model and year on our forum so we can look into the battery possibilities.
When buying a replacement motorcycle battery, make sure it has the same dimensions and terminal configuration as the old battery. Some motorcycle batteries available may be a few centimeter bigger or smaller than the original equipment batteries, which precludes the use of accessory battery covers. A few aftermarket battery sources caution that their products have the positive and negative terminals reversed. Some aftermarket batteries have terminals a few millimeter taller than the stock battery terminals.
When it was time to replace the five-year-old-battery in my motorcycle, I decided to get a maintenance-free battery and activate it myself. The surprisingly heavy box I brought home from the battery shop contained a dry battery, an acid pack, a sealing strip, terminal hardware, and a detailed instruction sheet (in English and Thai). The acid pack is quite clever. It consists of six slim plastic containers side by side, filled with acid and water mixed in the proper ratio for the new motorcycle battery.
At this point I must caution you about bargain batteries. There are dry batteries sold online and via mail order that don't include acid packs. I've seen dry batteries advertised for unbelievable prices. The drawback to this low price is that the customer needs to obtain acid and mix it with distilled water in the proper ratio. About 40 years. A do-it-yourselfer could go down to the local auto parts store or the corner petrol station and get enough battery acid to activate a dry battery. Finding battery acid in today's Bangkok automotive market would be a real scavenger hunt. The effort, expense, and stress of obtaining the acid would negate much of the savings. My advice is that if you insist on saving a few hundred Baht by activating a battery yourself, make sure the battery includes premixed electrolyte.