This happened to Me.It turned out, that the usb port had cracked loose and charger was not making good contact.After having usb port resoldered everything works like new.
Yes,the USB port cracks loose and takes a long time to charge because the contacts do not completely touch.You need to have the port re-soldered or replaced.
USB ports do crack loose over time and causing very slow charging.Try a different charger,sometimes works or connect to Your computer by USB to charge.If this does not work You need to have the USB port re-soldered.
The USB port does crack loose and charges slowly or not at all on charging.If You get the charging indicator and it won't charge or slowly charges,the usb port needs to be re-soldered.