Backup to iCloud no longer runs after update to iOS 8.2

Installed iOS 8.2 on iPhone 4s, auto Backup to iCloud no longer runs. Backup in Settings is ON. On WIFI, plugged in & locked every night for 7+ hrs. It worked perfectly every night on iOS 6 prior to the update to 8.2. I notice each morning when I unlock screen for the 1st time, it wants me to enter AppleID/iCloud password. Doing so has no apparent effect. Any ideas on how to fix?