Accessory Question about extended batteries

view story

http://androidforums.com – I've purchased some batteries from eBay and other sites that are either "Samsung OEM batteries" or slim extended batteries. I've noticed though that they either all discharge faster than the stock battery the phone came with or they charge to a certain point then discharge while its still charging. I've come to the conclusion that this phone only likes the battery the phone came with. Any ideas? (General)