Best practice for daily iOS app to cloud sync?

I have a background app that has to upload small amount 开发者_JAVA百科of data (several kb) to the cloud every day. In your opinion what is the best way to trigger the upload?

Should I trigger it at specific time of the day or at some other event? What if the upload fails (airplane mode) - how long should I wait before I try again?

My app gets awaken every time the phone detects a region change (cell tower change), so I could use that as event. My main concern is battery usage.

Thanks, Ventsi

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Do it every 24 hours. In case it fails (no coverage?), try again on cell tower change. If this has succeeded once, revert back to 24 hour timer.