I'm having some problems with my ipad and charging it. I am having to leave it in charge for a lot longer, but when I take it out and want to use it the battery is still not completely full and goes down a lot faster than usual

I'm having some problems with my ipad and charging it. I am having to leave it in charge for a lot longer, but when I take it out and want to use it the battery is still not completely full and goes down a lot faster than usual. The other day, I had charged my iPad overnight so that I could take it to university with me for the day, and when I had switched it on the next day the battery was on 5% and I had not used it since charge.