Great question — answering as the UphillTech team:
According to Garmin , with a 30-minute tracking interval and extended tracking mode, the battery should last for 20 days. Turn the screen brightness down and turn it off every single night when you are in camp to further extend the battery life. On the other hand, the inReach mini battery is 1,250 mAh , one 10,000 mAh battery should provide at least 4 charges and then you could use the device for more than just a single message per day.
Full answer by Charlie Brumbaugh: https://outdoors.stackexchange.com/a/22502 (CC BY-SA 4.0).
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