A sunny windowsill didn't appear to be sufficient. Though the indicator said the XeMini Plus was charging, the charge level still showed empty after a couple of hours. Fortunately, we had better luck on an outdoor patio and on a car dashboard with the charger sitting directly in the glare while the sun was at its brightest. Of course, you'll have to be particularly careful in a city, where shadows from buildings can get in the way, and during the winter, when the sun is nearer the horizon (charging performance dropped in the late afternoon).
On our best day, we were able to power a T-Mobile MyTouch 3G for about 30 minutes after charging the XeMini Plus outside for about 90 minutes. That's not great, but it's respectable considering that it's green. What's more, we suspect that like the Puma Phone's, the XeMini Plus' solar panels are for topping off (or "trickle charging," as Revolve says) a device rather than delivering a full charge. The company says that it could take the XeMini Plus up to 13 continuous hours to collect a full solar charge. Unless you're in Alaska during the summer, that approach won't be practical for most people.
But even with that caveat, the XeMini Plus should be a convenient way to deliver juice to a gadget when you're away from an outlet. It can keep your mobile device from going completely dead on a camping trip, for instance, though we'd also recommend giving it a full charge with good old-fashioned electricity before leaving home. Just remember that sitting in extremely hot sun isn't good for any electronic device. Revolve advises you not to expose the XeMini Plus to temperatures above 120 degrees Fahrenheit (49 degrees Celsius).
Revolve promises that after a full charge the XeMini Plus will deliver 6.5 hours of talk time for the iPhone, 8 hours for a BlackBerry device (the company doesn't get specific as to which), 9 hours for a TomTom One, 7.5 hours for a Garmin Nuvi, 59 hours for an iPod Touch, and 75 hours for an iPod Nano. The suggested retail price is $99, but we expect most retail outlets will offer it for $79.