I've never liked the idea of the self-contained solar chargers because it means that the batteries will be sitting someplace sunny and hot. Rechargable batteries are expensive, and their cost reflect the energy put into manufacturing them. Thus, a charging setup that shortens their life means that you don't actually save energy, relative to charging them from the grid, for example.
If you're setting up your own gizmo, I'd suggest separating the solar panels from the batteries. Connect them with a cable long enough that you can put the batteries in a shaded, relatively cool place. Also, make sure not to overcharge them, that too will shorten their life. One solution is to use solar panels to charge a larger, lead-acid battery with a charge controller, and charge smaller batteries from the big one using a "smart" charger. Find a smart charger that comes with a cigarette lighter adapter for use in a car - many such models are available, some for less than $15. Rewire that to connect to your 12V lead-acid setup and you can then charge various small NiMH cells correctly.