Samsung Galaxy Tab — Why is my Galaxy Tab 4 not charging?

I have a Samsung Galaxy Tab 4 (SM-T330NU). For the past couple months, it has been charging just fine. But I must mention that there was always a red X on the charging indicator. Though it bothered me on the back of my head, I ignored it as my Tab was charging fast and everything must have been fine. But in the past two or three weeks, my Tab has been acting funny. I usually charge it overnight so these are my observations. Sometimes it charges to 100% and then after an hour of usage it is still 100%. And then when I let it rest for a while and checked it again, it read 37%. Sometimes it really charges to 100% and then trains super fast. Sometimes it charges to only 20% or so but drains very slowly. One day, it was 20% when I charged it and the next morning, it was 1%. I was shocked! And I've tried many ways while charging: Airplane mode, turning the Tab off. Yesterday, it drained to 1% and I charged it and now its stuck at 3%. If I unplug it, it drains to 1% in a few minutes. I've tried different things to hopefully charge it. I tried different cable wires, wall adapters, plugged it into different wall plugs around my home, plugged it to my laptop and still no solution. Is there something wrong with the Tab itself or is it an external problem I am not finding? Please help.