Hi Joe!
For a long activities or camping days, etc, I used a 9w solar pannel USB.
It allows me connect USB any kind of chargers, powerbanks, etc.
My rig is powered by 3x18650 cells that I charge with a USB charger connected to solar pannel.
There is a lot of brands but you must watch the real power VS power indicated, In this case, RAVPower has a very efficients pannels.