1. Most solar chargers use 1000 mAh internal batteries which seems ridiculous considering rechargeable AA batteries have between 2000 – 3000 mAh of current. NiMh batteries are inexpensive and pretty easy to find.
2. Because the rechargeable batteries put out 2.4 volts, a solar panel that gets at least 4 volts is required.
3. Cut off 1/3 of the wire from the battery holder and then strip some of the coating off. Next, cut off 8″ from your stranded wire, and strip the ends.
4. Wrap one of your 8″ cuts around the diode's negative end (it's the end with the black bar) and solder it. Solder the diode's other side to the solar panel's positive tab. The other 8″ wire gets soldered to the solar panel's negative tab.
5. Twist the red wire from the battery pack with the positive wire of the solar cell and the battery pack's black wire with the negative. Do not solder them!