It's here: http://bbs.imp3.net/forum.php?mod=viewt ... 5%E7%B3%D8
Stock batteries are claimed as being 5x50x68mm, the suggested replacements are 5.2x61x86mm. However, the picture shows quite a wasteful frame for speakers. My suggestion would be throw that white harness out and play with speakers a little.
Another approach is mentioned there: a disassembled sandwich of two batteries 71x69x10mm (2 batteries of 5 mm thickness) yielding 5800 mAh, price is 32 Yuan (which I believe is just US $5 for a two-pack): http://item.taobao.com/item.htm?id=8000110377
Well, I strongly believe that anyone knowing Chinese could find an easy cheap ~6000 mAh replacement with good fit, too, like in an hour of searches in Baidu.com
If we want to go into case modding, that's a whole different kettle of fish. Of course we can stick larger batteries than the stock dimensions allow, but I wanted to avoid that.
The speaker bracket can be dremeled to be smaller which can buy you maybe 1 cm in that direction, but the problem is the bottom of the case begins to slope upwards towards the edge of the housing which forces you to use a battery thinner than 5mm. We can start shaving off LCD guides to get us a bit more space in the other dimension. Maybe another 1cm in that direction if your lucky. The same sloping case problem here. The vibrator is located in that corner and that can be easily moved and the bracket can be removed too which gets you more space. You can hot-glue that vibrator just about anywhere, extending the leads if necessary.
I'm all for this sort of modding, but I would think the energy and time spent on something like this might start offsetting any benefit. If we can get the "new" Novo8 batteries, I would think that would be the most painless way of getting more capacity, even if it's not ideal for those who want 10hrs of wifi time.
I'm definitely for this kettle of fish. Especially when one can get the device for about $124 in China today (links in my blog). So, think about it as DYI project, for a DIY "kit" price.
In my blog, I'm collecting other Ainol Novo 8 "upgrading" ideas, and starting with batteries, some of them -- like rear camera -- might require a mod of back cover.
As for D2K enthusiasm on a "news" of all Ainols getting "new" batteries overnight, while leaving model number intact, plus dropping the price, I'm very skeptical. Not a single Chinese forum on Ainol Novo 8 has any idea about such a wonderful development, while dropping price tag. No, I think I remember one, but it just quoted that Centocose Ainol letter.