How tough are they.....Good question. I have not done anything serious with mine, so I can't be sure,but my impression is that they will do fine with reasonable care. If fastened to the exterior of a pack, the solar panels could be shattered in a fall or a hard bump against a tree. I suspect I will put them inside the pack when moving, and set the panels up when stopped.

For most trips, you will be lighter if you simply carry spare batteries rather than a charging rig, especially if you standardize battery types.