it sounds like you just need a new battery its really not hard and doesnt cost much you could do it yourself i got mine stuck in a boot loop it wasnt booting cause it didnt have enough power because my battery was crap changed it and it fixed it other then that you will probably not get anything out of it its dead
i would say just a new charger but if you already tried that then what i do is i just get a small pin needle and just poke around in the charging port for a while and dig out lint or even wood yes ive seen some wood in a charging port and just clean it out really good then try it and if not i would just put in a new flex cable charging port in it and try