If the "OEM" replacement battery you got isn't holding a charge very well, you probably got a counterfeit, or you didn't condition the battery correctly. (Charge fully, let it drain to 0%, then charge back to 100%, repeat, at least twice.)
Right now it seems the current recommendations for aftermarket batteries is either OSTENT or Cameron Sino.
I personally recommend Cameron Sino (make sure you get it from an ACTUAL DEALER and NOT Amazon / Ebay / AliExpres), but others in the past have expressed discontent for them because they died too quickly. Coincidentally enough, those that complained also got theirs cheaply from Amazon / Ebay / AliExpress.
A different mod ("Power Armour") to expand battery capacity by using the PS Vita battery instead, used to exist. They seem to have ran out of stock and puffed out of existence, though.