What is wrong with my iPad’s battery?

This has happening way too often recently. My iPad will shut down as if it ran out of battery percentage when it gets at low percentage (usually 40% or lower). It will not turn back on unless I plug in the charger. Then, once it turns on again, it will be at the same battery percentage as the percentage at which it “died”. I’ve also noticed the battery is also draining much faster than normal. For example, it was at 16% when I turned it off for a minute or two, and when I turned it back on, it was somehow at 9%. Another time, I was walking from one class to another, and the battery percentage dropped 10%. It was maybe a 5 minute walk, tops. What is wrong with my iPad’s battery, and how can it be fixed?

Thank you for reading.