We’ve tested bags with small solar panels for keeping your iPod or cell phone charged, but the Generator’s high-efficiency, 15-watt panel charges a removable 58-watt battery pack that can output up to 20 volts, enough to charge your MacBook. It’s a great idea that works OK, but it’s not going to replace your power adapter.

The 4.5-pound, briefcase-style bag isn’t exactly a looker, although we liked its comfortable mesh handle, heavy-duty zippers, and the metal D-rings on the corners, which you could use to lock it to a stationary object (BYO cable lock). Inside there’s a padded sleeve for a 17-inch ’Book, plus organizer pockets. But we didn’t understand the point of the zip-off back panel, and a couple of the headphone-cable ports didn’t go anywhere, leaving us scratching our heads.

The solar panels charge the versatile battery pack, but this takes five hours in ideal conditions--that’s strong, direct sunlight, with the panels angled toward the sun the entire time. In our normal routine, we found it near impossible to keep the Generator charged via the solar panels, although “gotta charge the solar bag” is a good excuse for a sunny-day beach trip. If you live in the desert--or anywhere safe enough to leave your $500 bag out in the sun for five hours--you might have better luck. The included AC charger can also juice up the battery pack in a couple of hours.

You double-click the battery pack’s button to select the voltage range: 3.5–5 volts (USB devices including the iPod and iPhone), 5.0–6.5, 6.5–8.4, or 12–20 (Apple laptops). Then you connect the required tip for your device to the battery pack’s DC-out or USB-out ports. Voltaic includes tips for LG, Nokia, Samsung, and Sony Ericsson phones, plus the iPod/iPhone 30-pin dock connector tip, and 12 universal adapters for things like Kodak and Canon cameras, Palm PDAs, and more (see www.voltaicsystems.com/generator_adaptors.shtml). The MagSafe tip for Apple laptops is a $20 add-on.

The battery pack has two LEDs: The charging-speed light is red for a fast charge (i.e., direct sunlight) and green for just a trickle. The battery-level light is green for a 70 percent or stronger charge, amber for 70 percent to 30 percent, and red for less than 30 percent--we would have preferred an actual numerical meter.

In our tests, keeping an iPod or iPhone charged was easy, but our laptop was another story. When connecting the battery pack to our MacBook Pro, we could only get a net increase in our ’Book’s battery charge if we left the lid closed, and even that was underwhelming: After two hours, our ’Book’s battery went from 20 percent charged to 40 percent, and the Voltaic pack was in the red. When we kept the Voltaic pack connected to our ’Book while we used it, the ’Book’s battery drained a little slower, extending our total-use time by an hour.