Have you checked, if there is enough time to do so, what the state of charge of the battery is? Have you tried charging it to fully charged-100% . (do this with the tablet switched off so that it won't take so long to do) and then seeing how it performs.
If you have done the above and you still have problems, try connecting the charger (switched on) to your tablet and see if the tablet remains on when you use it. If it does then your battery is probably failing and it needs to be replaced.
Even rechargeable batteries have a life span.
Try the following and see if this resolves the problem. This is not a master reset so your information will not be deleted.
1. If your device is on, turn it off.
2. Press & hold the Volume down button. While holding Volume down, press & hold the Power button until the device turns on. You'll see the word "Start" with an arrow around it .
3. Press the Volume down button until you highlight "Recovery mode."
4. Press the Power button to start recovery mode. You'll see an image of an Android robot with a red exclamation mark.
5. Press & hold the Power button. While holding Power, press the Volume up button once. Then release Power.
6. Press the Volume down button until you highlight "Wipe cache partition," and then press the Power button to select it.
7. Press the Volume down button until you highlight “Yes,” and then press the Power button to select it.
8. Wait until the cache is wiped. You’ll see the words, “Cache wipe complete.”
9. Press the Power button to restart your device.