That seems contradictory, doesn't it? Well, the power is free, but the power pack is not. A recent price reduction at All Electronics, however, has just put the solar-powered battery pack for the Game Boy® Advance within reach.
The SOLAR PAK™ (All Electronics #SPL-08) is a great solar panel platform that can power the GBA, as well as illuminate the screen with four onboard ultra-bright white LEDs. While the LED illumination is suspect (due to screen glare), the rechargeable solar-powered battery pack is a great way to hedge against battery landfill waste. Unfortunately, most SOLAR PAKs arrive with dead batteries. Fortunately, these batteries can be easily replaced. A PopSci Weekly Project hosted by Instructables can show you the step-by-step procedure.
The new, reduced price for the SOLAR PAK is $3.95. While you're shopping at All Electronics be sure to give a close look to the 400-foot spool of twisted 22-guage solid wire (#22TW-400) for $9.50 and the SEARS® Craftsman Model 82061 digital multimeter featuring resistance, capacitance, and continuity signal (#DMM-61) for $10.65. Then make All Electronics one of your regular stops in search of new project materials.