Please help me on a cell phone issue!

I have a plain samsung flip phone from alltel. I was about to go to bed and set my alarm I plug up the phone to charge it and all of a sudden it starts cutting off and the screen says “No more battery shutting off” or something to that extent. I had pretty much a full battery and its never done this before. I cut it on and it does it again. I did this about three times so I took the battery out and cut it back on it hasn’t done it again yet but this is my alarm if it cuts of in the middle of the night I’m Screwed in the a.m.!! Has anyone experinced this problem before and if so what the hell is wrong with it!!
Please help!!!<——-I know thats is a lot of exclaimation marks but I’m being overly dramatic like I do sometimes. I apologize. (Also I know my grammer and spelling probably isn’t perfect overlook it. I don’t have time for spell and grammer check!) THANKS