The majority of solar lights on the market are powered by a solar panel that recharges a lithium-ion battery pack. you can use them if they don't charge outdoors or include a USB charging port to refill the battery bank in overcast weather. When shopping for outdoor solar lights, remember that the solar panel should be placed in direct sunlight to fill the battery bank. If it's going to be used to line a path with a wide-open view of the sky - chances are your light won't have an issue charging. If your light will be placed in a shady area, look for lights with detachable solar panels that can be placed in a spot with direct sunlight. Alternatively, a solar light with a larger solar panel will charge better in lower light conditions.