Heavy iPhone users know they often need to call for (battery) backup.

The daily recharge is a scenario familiar to iPhone users. Most days, we’re not far from the trusty USB ports on our Mac or a plugged-in USB AC adapter, so the need for constant recharges isn’t too much of a problem. But every now and then, we’re out and about all day, which makes juicing up our phone more problematic. Especially since it’s those days when our iPhone usage tends to be heaviest: sending and receiving lots of email, taking pictures, and killing time between meetings by watching video. For recharging while on the road, Just Mobile’s Gum battery pack is a small, lightweight, and-easy-to-use charger that can double your iPhone’s battery life, and also works for your iPods and other USB-charging accessories.

The Gum comes in at a svelte 2.5 ounces, making it perfect for adding to a laptop bag--or just slip it in your pocket. And since it’s about the size of, well, a large-ish pack of gum, there really isn’t anywhere the Gum can’t go. It charges via an included USB to mini-USB cable and adapter, and three LED lights offer an indication of how much charge remains in the Gum’s battery. The four-step scale (three, two, one, or no LEDs lit) isn’t a crucial feature, but it did come in handy for quick checks of our remaining juice. We were able to fully charge the Gum via our Mac’s USB port in a couple of hours--optional AC and car adapters are available from Just Mobile.

In our tests, the Gum was able to charge our iPhone almost twice, in keeping with the specs of its 2200 mAh battery. While the design of the Gum required us to also carry around a charging cable--unlike other battery packs with a built-in dock connector--the added flexibility of being able to use the Gum to charge other devices was an acceptable trade-off. And though we used it most for our power-hungry iPhone, the Gum works just as well for iPods, Bluetooth headsets, rechargeable speakers, or whatever else uses the 5V USB charging spec. The only thing we didn’t like was the on/off switch, which must be flipped when charging a device with the Gum.