The Backup Battery also has a Micro-USB connector that's attached by a short cord. Thankfully, that makes it compatible with most non-Apple phones and tablets these days, but you'll be out of luck if your device has a different port (like Mini-USB). Similarly, while the Micro-USB connecter slides into a slot on the side of the battery, it doesn't fit quite as snugly as I'd like. On the battery's opposite end are a Micro-USB port (more on that later), a small power switch, and four green lights that show the Backup Battery's power level.
In my tests, the Backup Battery performed exactly as promised. I first placed it on a charging mat and used it to power both an iPhone 4 and an simultaneously. Boosting both handsets took no longer than when using a wall charger while the Backup Battery powered up in the same amount of time.
I then took the Backup Battery to the office and used it to completely charge an almost-dead iPhone 4 without any problems (with a 1,850mAh battery inside, it can almost double the life of most smartphones). Even better, once the Backup Battery is dead you can charge it again by connecting it to a computer via the included USB cable (that's where the aforementioned Micro-USB port comes into play).
When I reviewed CNET's first PowerMat product in 2010, I didn't quite see the point of paying $100 for a fancy accessory when you could just use the free charger that came in your phone's box. That's still true to an extent, but after using the Backup Battery for a couple of weeks, I can see its appeal.
Indeed, charging two devices at one time is convenient and I like how the Backup Battery turns off automatically once it and your handset are fully charged. So not only do you avoid overtaxing it, but also you save energy and money off your electric bill. What's more, the Backup Battery's ability to zap your precious gadgets back to life when you're out and about can be a lifesaver.
Like PowerMat's other products, the Backup Battery doesn't come cheap ($49 for the black model and $39 for the white version). Though that's a reasonable price on its own, remember that the company's charging mats cost an additional $29 to $59. Of course, you don't absolutely need a mat to use the Backup Battery (there's always the USB cable), but then you won't really get the whole PowerMat experience. And if that's the case, you're better off buying a cheaper emergency battery that will work just as well.
When you add everything up, the benefits of PowerMat's products still don't completely outweigh the costs. But if you're looking for a unique and functional way to charge you gadgets in multiple places, the Backup Battery does the trick.