Why is my 4s not holding a charge

I put my 4S on the charger on night and when I woke up the next morning I only had 25% battery. I needed to use my phone that day and so I had it on the car charger most of the day. When I would use my phone while it was plugged in the battery life would lower and and when I was not using my phone It would stay the same and not increase the battery life at all. That same night the battery died completely and whenever I plugged it (tried several different power sources) it did not have enough power to turn on.