Battery drains a lot after iOS11 update My iPhone 7 used to consume 3-4%  of battery in standby mode but after upgrading, it is consuming 40-45%  of battery in 10 hours of standby mode. What shall I do?
You are not alone (https://duckduckgo.com/?q=ios11+drains+battery), and usually this happens with all major iOS upgrades. Besides following the usual steps to reduce battery usage the probably only course of action is to wait for iOS updates.