What is wrong with my phone?????????

[AC Question]

Hello, I am having problems with my Samsung galaxy s3 and I need immediate help. Recently my usb charging port has not been working. I cleaned it with a toothpick and lint came out but that still did not solve the problem. So my next best thing was to do wireless charging by cutting a usb cable and attaching it to the back of the phones wireless ports. It works but my phones battery dies super fast!! Then I figured out my battery was bad by doing the spinning test so I bought a new battery and now the battery is good BUT my phone randomly shuts off at around 70-80%. Then when I turn it on it says 8% but when I turn it off and take the battery out and place it back in and turn the phone on it goes back to around 75%. I DON'T UNDERSTAND WHAT IT WRONG WITH MY PHONE! If someone can please assist me I would greatly appreciate it..

 

[Rukbat]

Next time it shuts off, turn it on, go to Settings.General/Battery and tap the graph at the top. Look at the graph on that page for a sudden drop to zero. If you see that the battery has a dendrite and is defective. (Since it's new, they should replace it.) For more than you wanted to know, see Lithium Battery Dendrite links.