The Primo Cube measures about an inch and a half square and a little short of an inch thick, meaning it isn't quite a perfect cube but it has rather more heft than your average square. It's well thicker than most modern smartphones, even the somewhat chunky first-gen Motorola Droid that was our primary guinea pig here. We think it's perhaps a little too bulky to use as a keychain, but we've certainly seen people have bigger things dangling from their car's steering column (mom). Regardless, it's small enough to stick in your bag and forget about it.
This slight chubbyness leaves room for two flip-out connectors on the back, mini- and micro-USB for compatibility with nearly every (non-Apple) mobile device produced over the past four or five years. You can juice up anything you like without dragging any cables along, but rather sadly there's no flip-out, full-sized USB port to recharge the Primo Cube itself. It does have both mini- and micro-USB inputs, though, making it a little easier to top up.
We charged up the Primo Cube for its first use and were pleasantly surprised to find that the mirrored finish doesn't just display a pretty face. Behind it are four light-up shapes that indicate current charge. Once charged (about an hour and a half from empty) you can pocket it until needed, then flip out either plug and dock it to your mobile device of choice.
For testing we left our Droid blasting our favorite deathcore classics until it powered itself down mid-scream. We then popped in the Primo Cube and turned the phone back on again, which initially showed a five percent charge. The four LEDs on the Cube counted down and, after about 90 minutes, showed empty. The phone's 1,400mAh battery now read 30 percent full according to the OS.
In another test we again drained it as far as the Android would let it go, enough that attempts to turn it on again were ignored. Again in went the Primo Cube but this time we booted it up immediately, with no time for charging, and were able to make a 60 minute phone call without issue. The phone didn't really gain much charge while we were yakking away, but it was a good indication that, in an emergency situation, you can certainly dial home on a dead phone with a Primo Cube.
The PhoneSuit Primo Battery Cube isn't a perfect product by any means. At $40 it's little cheaper than your average replacement battery for your average phone or other mobile device, and it also takes up more space in your pocket. But, it's still plenty portable and, if you have various gadgets that may need charging at various times, it certainly is a flexible way to add a little juice to whichever device needs it most.