Yes there has been ALOT of fake battery's and battery packs sold on DX, i remember buying a 10000mAh battery pack/usb charger, and others that have bought the same sku had posted pics of the battery's inside, and mine was different from theres even thou it was the same sku.
That sku had iron plates in it to simulate bigger heavier battery's so that i would feel like you where getting 10000mAh, but the battery's inside was 2x 800mAh, i was "lucky" i got the one with the 2x 1500mAh battery's.....

But after some 150+ orders from DX i know what i buy now a days. I generally only buy things that are really cheap and things that i cannot get at home.....