Go into Settings-Battery and look at the values, usually around 45-47% use. Or feel how hot the phone is.
Suspect a memory leak or something always running in the background.
Run standard performance test/tools with XCode, please.
Still eating massive amounts of battery power, 72% on my iPhone just now. While waiting for them to fix this nasty battery eating bug, you need to double-click and swipe out Memrise the app so it’s not in the running stack. Jus in case you wondered why your newly charged phone suddenly dies…