how long are you looking at being off the grid?
I use something similar to this and it can get you a couple hours at least if the iPad was fully charged to start with. https://www.amazon.com/Portable-TSA-approved-Jackery-PowerBar-Compatible/dp/B076DXWPHS/ref=sr_1_3?ie...
you can go with a deep cell car battery and then add an inverter for even longer run times. https://www.amazon.com/NEW-SUN-Inverter-110V-120V-Outlets/dp/B07BVQJWVS/ref=sr_1_8?ie=UTF8&qid=15505...
