There are many options for solar recharging batteries. Years back I picked up several compact solar chargers that'll do AA, C, D, 9v, and "prismatic" batteries, whatever those are. It has a meter to give you an idea of sun strength too.
Later on I picked up a small panel with multiple voltage taps and battery holders that'll do the same, only quicker, plus be able to power small devices.
This was years ago, so I'm sure there are a lot of better products than what I have.