Samasung S4 repairs

I sent my samsung s4 in for repairs 15/02. The motherboard needing replacing (wi-fi not working). I Collected the phone and was informed by the technician that the phone was repaired but not charged. I had a portable battery pack which I used. The phone did not charge immediately but I lift it in my car's glove compartment. The evening I noticed that the phone was charging intermittently (on/off) all the time. I returned to Samsung smartcare centre where the technician informed me that there was nothing wrong with the phone after he plugged it into his charger. He suggested that it was my charger or battery pack that was the problem. I left and again tried charging my phone with no success. I again returned to the service centre and asked for my phone to be repaired. I was then told that it was my battery that was faulty. I enquired as to how this could now be the problem as there was never a problem with my battery before I brought the unit in for repairs. I also enquired as to whether a record is kept of the original battery. I asked for the manager to contact me with no response. I bought a new battery from the service centre which also works intermittently.