That's the thing I made. I'll edit this post with more detailed information later.
DIY External Power Pack_cost accounting
| Meterial | Count | in CNY | in USD(6.4:1) | Comment |
|---|---|---|---|---|
| Box | 1 | 0.00 | 0.00 | from a box of Hershey's |
| Wire | 10 | 0.15 | 0.02 | |
| Glue stick | 3 | 0.90 | 0.14 | |
| Battery | 1 | 20.00 | 3.13 | 3.7v/3700mhA |
| protective circuit for battery | 1 | 3.80 | 0.59 | |
| Solar pannel | 1 | 6.80 | 1.06 | 4.5v/78mA |
| Schottky diode | 1 | 0.50 | 0.08 | ID 5819 |
| booster circuit | 1 | 8.00 | 1.25 | pre-made, output 5V/500mA |
| LED | 1 | 0.10 | 0.02 | |
| Resister | 1 | 0.02 | 0.00 | 2.2k |
| USB mini port | 1 | 0.28 | 0.04 | |
| self-lock button | 1 | 0.33 | 0.05 | 7*7mm |
| capaciter | 3 | 0.06 | 0.01 | 1up |
| Battery Charger IC | 1 | 9.00 | 1.41 | MAX1555 |
| bread board | 1 | 4.00 | 0.63 | |
| Total price | 53.94 | 8.43 |