GB/T18287-2000 is the "execution standard". V5-364560 should be the model number. I checked against my battery, and the number does match up to the physical dimensions of the battery (approx. 45mm x 60mm x 3.6mm). However, even if you find a battery with these dimensions, you're probably not going to find one with the right connector. If you want a replacement battery, it would be better just to buy one from Astak so you will know for certain that the battery you are getting will work with the device.
Hopefully, since there are other companies who are going to be selling the Hanlin V5 (Bebook mini for example), the replacement batteries will be easier to find in the future, especially those of you who are overseas.
Robertb, any idea if Astak is planning on putting the battery (as well as replacement covers, cables, etc..) up for sale on the website, or is it just going to be the case that you will have to contact support to buy one? (I see that in the FAQ, you have instructions to contact support regarding replacement batteries.)