it's curious, after update the battery drains faster than before.
Experiencing it as well. Drains at double speed than it used to.
I have the same problem and have tried what you have suggested - makes no difference. In any case what you are suggesting is NOT the answer. A 1000GBP phone that's less than six months old should not have such degraded battery performance. My indicated battery life (full charge) has deteriorated from 36hrs to 20hrs.