Why iPhone 6 performance so slow after ios11
Why iPhone 6 performance so slow after ios11
aKMYpaTfrombrest,
Hmm, you probably have a rogue app constantly running in the background.
Go to Settings > Battery and scroll down to BATTERY USAGE to see the apps that are consuming your battery. If any of the apps have unusually high usage they can be shut down (double tap the Home button, scroll left or right to find the app, then swipe up to shut it down).
If no help:
Make sure that your are on iOS 11.3 and check "battery health beta" in: iPhone Battery and Performance
If all else fails, consider a battery replacement: