Been using this for several days now and it works as advertised with my 9800.
Best place I found was on the dash of the car. It ran several hours and charged the battery with no problems. But the charger is very slippery and tends to slide around and off. A less slick back cover or e-grips would really help. Also placed it on the sunroof cover and pulled it closed to keep it in position. That seemed to work as well, but the USB cable was a bit short.
The charger has to be in direct sunlight for several minutes before it will actually start to charge. Makes sense as it has to build up enough power to get going. Any cloud cover and it knocks off and seems to reset it self before it gets back to charging.
All in all, I am happy with it. Works as advertised, but it is a slow charge. Comes in really handy when you have no plug available and you need a bit of power.