You could be experiencing this problem due to a range of factors. One option is that your battery could be going bad and will need to be replaced, however that is a last resort fix and should be avoided until you run out of other options. I would first try some other possible noninvasive fixes. Try turning down your screen brightness and turning off your Bluetooth when not in use. Avoid running your device down to the last percentages of battery as this reduces the life of the battery dramatically over time. If you enjoy using your tablet while it is on the charger this can contribute to a shorter battery life for the devices current charge.
The charger could also be the issue. If you are not using the cable that came with the device as it's primary charging cable this could be a contributing factor. If you are using a third party USB cable that plugs directly into an outlet the improper voltage/amperage can harm the battery permanently. Make sure you are using the correct charger for your devices. Depending on the device overnight charging can be harmful as well.
There are many factors that contribute to a rapidly dying battery, most of which are preventable by changing a few habits surrounding the usage of your tablet.