Screen brightness is a huge drain on the battery, so reduce your iPad screen brightness as much as you can tolerate.
Have you tried a hard reset of your iPad by holding down both the Home and sleep/wake buttons until your iPad goes to black and restarts with Apple logo, then release the buttons?
How much free data storage space is left on your iPad?
iDevices need to maintain, at least, 3 GBs, OR GREATER, of free data storage space.
In Settings App, Battery, check to see if any apps/processes are eating up your battery.
In Settings app, General settings panel, turn OFF Background App Refresh for any apps that you feel do not need constant updating in the background
In Settings app, under General settings, Reset panel, at the right bottom of the list, Reset All Settings.
In Settings app (NOT from the iOS Control Panel) turn OFF Bluetooth when not using any Bluetooth devices.
Also, in general, if you want a faster IDevice, on all of my iDevices, I turn off most of the iOS motion graphics eye candy, by simply turning ON Reduce Motion in Settings app, General, Accessibilty settings.
Make sure you aren't running scads and scads of background apps in the iOS 11 Control Panel/App Switcher.
If you are, you need to quit the bulk of these background running apps by tap and hold a finger on an app window in the switcher and slide your finger upwards to quit an app. You should be able to use more than one finger to quit more than one app window simultaneously.
Also, make sure you don’t have scads and scads of active website tabs running in the web browser.
If you do, greatly reduce the amount of active website tabs your web browser.
Having an iDevice streaming content while continually going out to the web to update app info will eat up both processor/RAM cycles as well as eat into battery cycles, too!
