Finally! I have a solar charging system for backpacking that actually charges anything, including the big batteries on my Canon full frame dSLR! It's tricky because many camera batteries are 7.4V or 7.2V far more than the 5V of most USB devices. The good news: once I found something that could charge at 7.4V, it had no trouble with my phone, AA and AAA batteries and all other 5V USB devices!