Again, I have the opposite battery performance with my 64 GBs iPod Touch 6th gen.
I use a smartwatch connected to my iPod Touch 6 and Wifi and Bluetooth are always on.
I get between 10-12 hours of constant use and if I just leave my iPod just working behind the scenes with just my smart watch, I get between 16-20 of battery life on a charge.
Things to check for.
Make sure screen brightness is lowered to a brightness you can tolerate.
In Settings app, General settings panel, turn OFF Background App Refresh.
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.
Good Luck to You!
