I purchased a battery off Amazon 2 months ago for my Epic 4G.
I noticed the reviews and other people have posted good things using the battery with the epic 4G.
I was looking for a spare so I could switch the battery out when i was on the go. I guess it doesn't help that I am addicted to my phone.
The battery is still giving me good life and would recommend it.
Amazon.com: Premium Lithium-Ion Battery (EB575152VA) for Samsung Galaxy S (Epic 4G D700 (SPH-D700), Captivate i897 (SGH-i897), Vibrant T959 (SGH-T959), and GT-i9000) and Samsung Focus i917 (SGH-i917): Electronics: Reviews, Prices & more