Hi Isaak,
On Android, there is a Mission resume and multi-battery flights feature, which allows you to continue an interrupted mission.
On iOS, the same feature will be implemented in a new app version that will be released by the end of December. The latest information about this upcoming feature on iOS is available in the forum topics How to resume mission after battery change and Pix4Dcapture - Large site/Multiple flight Missions?. Please post any questions or comments there.
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