I would assume they are using the same cable they used to be able to fast charge with. Changing the charging port seems like it could work. I have replaced my battery after it started discharging quicker than it used to. Also at that time fast charging stopped working. I have to keep it in medium power saving mode for it to last more than 3-4 hours.
Oh i forgot to post the fix to this issue. I was so happy when i found an answer. There was this forum with somewhere near 80 pages of answers and comments. In the middle of it was a solution to repair a small micro fuse located just below the cable that goes from the main board to the digitizer board. If you notice carefully it can get burnt. This happens when the unit is not powered down and the digitizer is detached or disconnected. I could not power mine down so i thought because the digitizer was unresponsive to touch. But what i did not know is there is a shutoff switch near the power button. its a slide switch. So once i figured out what the issue was i ran a super fine wire from one side of the micro fuse to the other and soldered it in. It was tough but it worked!!! like a champ. Hope this helps any with this issue. I spent a lot of time and money when it was just simple fix.