GBA Solar Pak
Gemini's Solar Pak attaches to the original Game Boy Advance unit via the battery casing and accessory clips. The unit comes with rechargeable batteries, and more importantly, a solar panel that can be used to recharge the battery pack under any light source, be it the sun or your desktop lamp. The solar energy is used to supplement the power that is drawn from the battery supply, and recharge it. An optional AC adapter can also be used to recharge the battery more quickly.
The Solar Pak carries an MSRP of $29.99.