旅途中备份照片，又不把流量吃光

We would not turn it off entirely. The point of backup is having a copy if the phone is lost or broken, and that risk rises while travelling rather than falls. The better setting is Wi-Fi only, combined with leaving the phone on charge overnight so the queue completes. You get the copy without spending the plan.

Usually because another service on the phone also backs up photographs and has not been configured: a document-focused cloud drive, a manufacturer app, or a chat app that saves images into the album where something else then syncs them. Open the data statistics screen sorted by volume; whichever name appears near the top despite you barely using it is the one to deal with.

The honest answer depends on how much you shoot, whether you film, the resolution you use and the file format your phone writes, so we will not offer an average that would mislead your planning. The more direct method is your own history: look at what the photos app consumed on a previous trip, or work through our data calculator and then allow more than it suggests.

Yes, and it is often the best option, since you are not using the phone anyway. The important part is keeping it on charge, because uploads stop when the battery falls, and starting with the pictures that matter most in case the night is not long enough. If the connection genuinely cannot cope, copy to another device instead, which needs no internet at all.

There is a real risk, because anything not yet uploaded has no copy anywhere else, so deleting it removes the original. Confirm the pending count has reached zero and open a few of the images in the destination service before clearing anything. The same rule applies to copies made onto a laptop or a portable drive.

Take video out of automatic backup first, because the files are heavier than stills by a wide margin. Let photographs sync normally on Wi-Fi and handle clips in batches when you find a genuinely good connection, or copy them straight to a laptop or portable drive. Dropping the recording resolution one step for the trip also helps a lot and still looks fine for memories.

No: they remain on the device. There is simply no cloud copy until backup runs again.

Avoid it unless necessary: the upload simply draws on that phone's plan, which is a common way allowances vanish unnoticed.