Step 1: Tools and materials
Pliers (or muiltitool)
Clear packing tape
Lithium polymer battery charger (the original one specified was discontinued)
For better performance use the Adafruit Solar Lithium charger (connections are similar but it's slightly larger- see update below)
3.7v 2000mAh Lithium Polymer battery
Small solar cell
2" x 3" adhesive backed Velcro
Small double sided adhesive squares
7/10/10 UPDATE: Adafruit now also sells all the parts you need to make this a bit more mighty. Have a look here!
7/18/11- ANOTHER UPDATE: Adafruit recently introduced a new LiPo charger that is specifically designed for solar charging that has much better performance. It's not as small but the performance gains make it worth it. Have a look and read about the design here-
The single cell Lithium Polymer charger can accept input power that ranges from 3.7 to 7v maximum. When the cell reaches full charge the charger will automatically switch to trickle charging. When charging using the mini USB port, the charging current is limited to 100mA. When charging using the barrel plug jack, the charging current is limited to 280mA.
The solar cell maxes out at approximately 5v @ 100mA in bright sunlight. If you need faster charging simply use a larger solar cell- a 6v cell @ 250mA would work very well and they are easily obtainable and inexpensive. I used the size of solar cell that I did because I wanted it to be super compact.
I could not find out from the manufacturer if the solar cell I used has a blocking diode. A blocking diode is used in many solar charging systems to prevent the solar cell from draining the battery during low light conditions. Instructables member RBecho pointed out that the charging circuit used negates the need for a blocking diode in this application. You can tell when the solar cell is producing enough power because the little red LED on the charger will come on during charging.