I just recently purchased a used Samsung Galaxy S4 online a couple days ago. Everything was working perfectly fine until yesterday. My phone was at 17% last night and I plugged it into the charger. I woke up this morning and it went down to 15%. Whenever I plug in the charger, it shows a grey battery with a lightning bolt symbol but it doesn't turn green or it doesn't charge at all. It also says 15% charging on the lock screen but it doesn't ever go up. When the screen is off, it shows a red LED light at the top. The only problem I can think of is that I dropped it lightly two times about 3 feet off the ground. It was also raining a couple days ago and my S4 got a little wet but other than that, I'm completely clueless. My phone is currently at 7% but I'm afraid if I keep it on, it will die and never be able to turn on again. Can anyone please help me!