If you're travelling to Singapore or Perth, batteries are no problem.
For Singapore, practically all coin type cells can be purchased at stores selling watches, camera stores and film developing stores. Camera stores and film developing stores should also have all the bigger lithium batteries you want (CR123 for example). Supermarkets (Fairprice, Cold Storage) will carry almost all the usual alkalines batteries (AAA, AA, C, D) and may also carry lithium AA, CR123 and CR-P2 (the two CR123 packed together configuration) batteries. Department stores may also carry batteries but may be harder to find as you need to look for a hardware section. Needless to say, there will be a small selection of batteries in the toy department as well. Electronics appliances stores such as Denki and Harvey Norman will also carry a selection of batteries depending on the products they sell at that store. Finally, another place to look is in hardware shops, more commonly called DIY stores. These can be found in most shopping complexes and are not to be confused with the proper hardware stores found in housing estates.
In Perth, hardware shops will carry a good selection of batteries as will shops like KMart, Woolworths and Dewsons. Camera houses will also be a good source for coin type cells and lithium cells as well as the smaller alkalines (AAA, AA). Chemists will also carry a good selection of the smaller alkalines and all sorts of lithium and coin cells.
Hope that helps.
BTW, if you are coming to these parts, do let me know. My email address should be in my profile.