I have been checking out the utube videos of home experimentation with solar cell battery charging. most of the ones I've been checking out were cannibalized from solar garden lights. ( and their battery charging control printed circuit- about 2" square- these also come with one rechargeable battery to boot!)) the cell it's self is usually about 2" square. Under ideal conditions the charging rate seems like it could fully charge two or three AA's or AAA batteries in about 7hours. seems small enough that one could sew one to a backpack and get by with it, on a multi week hike. if your power requirements matched. I'm not sure how you would go about protecting the cell from damage, other than being very careful.