Almost a couple of years back, Google introduced its photo sharing and storage service called, Google Photos. Since inception, it used to have an option to back up photos when the device was plugged in and charging. It has recently been noted that Google has pulled off this feature from its Photos app on both Android and iOS devices.
Since this feature is no longer available, the only option you are left with is to turn off cellular data backup and make sure that no backups are performed while you’re roaming. You also need to check that photos and videos backups will only happen over a Wi-Fi connection.
There doesn’t seem to be any logical reason removing this important feature from the Google Photos app. You may choose not to update the app if prompted, however, if already updated, you just need to wait for Google to bring back the lost feature.
While this forfeited feature gives a hard time to the users, we expect Google to restore this feature as early as possible.