There are no user serviceable components in an iPhone nor does
Apple sell replacement parts. Any such items you see for sale are
salvage from stolen/broken iPhones or counterfeit.
Make an appointment at the nearest Apple store to have your iPhone evaluated.
Once the diagnostics are complete, the staff will explain your options.
Make a Genius Bar Reservation
http://www.apple.com/retail/geniusbar/
If you are attempting to charge using the USB on a computer, not all
computer USB ports provide enough power to charge the iPhone.