Definitely a power bank. I fly with a GoPro mounted over my shoulder, so it can see the instruments and out the windscreen as well. I use it for debriefing my flights, and if the worst happens it can act as a black box since small aircraft lack them. In my plane, the GoPro shares a 26,800mAh power bank with any cell phones and backup 2-way radio. My iPad is connected to a 10,000mAh or 26,800mAh power bank, which leaves the iPad's internal battery as the backup.

The bigger problem is that GoPros and iCrap devices overheat easily in the sun.