It's your charger cord. The part that plugs into your phone gets loose and wears out. The red LED lights but it's not charging. I had this problem and bought many cords. I found a charger cord on Amazon that has a piece that remains in the phone and connects to the cord magnetically. Problem solved for $8. Type in magnetic phone charger cord.
Please try to give a substantial answer. If you wanted to comment on the question or answer, just use the commenting tool. Please remember that you can always revise your answers - no need to answer the same question twice. Also, please don't forget to vote - it really helps to select the best questions and answers!