People who believe advertised numbers like these need to do more research on batteries. There is a huge discrepency between advertised mAh ratings to actual realworld mAh. Under actual usage tests some batteries that are rated at 2000mAh perform worse than some that were advertised as 1800mAh. The proof is in the pudding...
PC-Engine speaks the truth - for cheapo (quite often counterfeit) batteries, the mAh rating can be bullshit. Given the size of this battery, it seems unlikely - I guess we'll find out when the first reviews come out.
I'd rather take one of those battery/charger/case combos, they have even longer battery life and as a bonus you get the hard case.
Like the Nyko ones: http://gear.ign.com/articles/629/629388p1.html