Mail Background Activity Draining Battery

iPhone 6, 64GB

Mail Background Activity is draining battery. I currently have an Exchange account, Gmail and iCloud account. Exchange and Gmail are set to "FETCH" and iCloud is set to "MANUAL".

The most interesting part is the in the battery usage meter--the "USAGE" is always within an hour of the "STANDBY" time after charging to 100%--all apps closed--location items mostly disabled. Battery will drop 20-30% overnight and Mail Background Activity is always at the top.

I am on my second phone. After 3 reinstalls of the OS nothing seems to be working. I have narrowed the culprit (after activating email accounts 1 by 1) that the iCloud account is likely the problem.

Have tried turning off various iCloud functions but none (other than disabling iCloud altogether) fixes the issue. Anyone else have a similar issue?