The Battery Just In Case is a $40 iPhone case with a battery and a solar panel. I love the idea, but I'm not sure the phone-size solar panel is enough to get more than a tiny amount of electricity in any reasonable amount of time. (You can also charge the battery by plugging it in, like any such battery.) The company says they're working on supporting Samsung phones, too.
The Sunny Case opens to offer two solar panels. That should be better.
Powerup offers one-panel charging cases, but they cost $100 each.
Amazon sells probably dozens of solar cases.
Are they worth buying?