It's tough to pinpoint the expected battery consumption the Mevo app will use during your event. Much of this varies from phone to phone as well as each individual's use of the app (lots of editing versus few edits, lots of movement versus static video, etc.)
However, it's expected that your phone or tablet's battery will drain faster than it may when using other applications. To help preserve your phone's power during an event, try the following:
In addition, if you aren't near a wall outlet, you can plug your phone's charger into the USB port on the Mevo Boost. Make sure the Boost is on if you're doing this.