battery life iPhone SE poor

The battery life on my iPhone SE is poorer than its predecessor, a 3 yearold iPhone5. The SE is 11 months old, and needs a recharge in 7 hours of use. Does the battery need replacement and is this under warranty in the UK?

I have performed all updates in a timely fashion and tried all methods of reducing battery usage by apps. One day the battery percentage display dropped from 45 to 36 % in less than a minute for no apparent reason.

Mail frequently closes down when I delete an individual email

Screen view shudders

When at home, I get a message saying I need to input my wifi password, yet my wifi is working.