Most of the CREE lights run on 8.4V
The most common small solar panel is 12V.

You can buy extension cords for the CREE battery packs that you could build a connector with. As far as I can tell, the battery packs come with a charger controller and an over voltage cutoff.

What I haven't tried to do is to connect a small 12V panel into an 8.4V pack. If it was lead acid, the battery pack would pull down the voltage of the panel, and the panel would raise the voltage of the battery pack. I'm not quite sure what would happen with the Lithium batteries.

Perhaps it would be ok with a small panel. How many days a week are you using it?