why is it my Iphone 4 shutting down whenever I unplug it from its chord?

I have iPhone 4 (IOS 7.1.2), sometimes it is charging normally, but most of the time the percentage is not increasing. it remains (12% e.g) for about an hour. and when i try to reconnect the chord of my iphone it will automatically turns off and hard to open it again, and i found out that i need to shake my phone again before i able to open it and continue charging, but sometimes in (40% ) it will happen again, and the date and time resets when it open..and because of that problem I need to look on my Iphone when charging, to be able to complete and to fully charged my phone. the service warranty of my Iphone already expires. how can I fix this issue?