Taking the back cover off reveals a battery, like most other phones on the market today. This battery actually comes out with ease. The iPhone 4 is manufactured in a way that is opposite of the 3G, and 3Gs, but similar to the original 2G iPhone. Let me explain what I mean here….
iPhone 2G/iPhone 4 – In the manufacturing process, the Glass is the first part that is assembled to the chassis/frame, followed by the internals, and last the battery then the back cover.
iPhone 3G/iPhone 3Gs – The back cover is the first part assembled, then battery followed by the internals. The glass is the last part that goes in.