Yellow triangle with! In the middle

Samsung note 4 my daughter was playing a game on her phone and all of a sudden it came up with a yellow Triangle With an ! In the middle of the triangle and i don’t understand what’s wrong with it the other day I put a new battery in it and it was working fine for a few days then it wouldn’t charge kept saying 1% so I put the original battery back in it and it was working fine and charging and now this I don’t understand does anyone know how to fix it and will it cost a lot to get it fixed ? Please can some one help me please