Mophie's Juice Pack battery line offers a variety of options to power up your iDevices when you're away from an outlet. They deliver on-the-go power, but can be a bit bulky, the add on phone cases especially. A more-pocket-friendly solution—the Mophie Juice Pack Reserve for iPhone and iPod ($34.95 direct), could be mistaken for a cigarette lighter—but inside its small shell is an add-on battery that provides a quick burst of power when you're in a bind.

The Juice Pack Reserve is lightweight and compact, measuring just 3.0 by 1.5 by 0.5 inches (HWD) and weighing 1.6 ounces. The top flips off (think Zippo lighter style) to reveal the 30-pin Apple dock connector. Along the side is a cleverly hidden USB connector, attached by a rubber strip that tucks neatly into the bottom of the Reserve. On the opposite side is a button to activate the battery status LED, but instead of multiple lights to indicate charge level, the Reserve uses a single LED that changes color depending on the charge. Below the battery button is a key ring, so you can attach it to your keys to prevent it from going missing. The Reserve shares the same soft-touch, rubberized plastic construction as its bigger siblings, the Juice Pack Boost ($49.95, 3 stars) and Juice Pack Powerstation ($79.95, 3 stars).  

Unlike the Scosche FlipCharge Burst ($49.99, 3 stars), the Reserve cannot simultaneously sync and charge your iDevices. It packs a 700mAh battery inside, which is a lot smaller than most external batteries. However, much like the FlipCharge Burst, the Reserve is not meant to be a full-on power supply, but rather a quick fix when you really just need a small charge to keep your device going until you can properly charge it. In my tests, the Reserve added 3 hours, 33 minutes of 3G talk time to our Verizon iPhone 4S. The Burst, which has a slightly larger 720mAh battery, added just 3 hours, 17 minutes.

The difference in battery size is negligible, but the design and build quality of the Reserve is better—plus it's $15 cheaper than the flipCharge Burst. It's still a bit pricey for the capacity, but you're paying for portability and attractive packaging. Though it's still too large to take a permanent place on my keychain, I could see throwing the Juice Pack Reserve in my bag while traveling for an extra boost. If you want a more serious power solution, a battery case, like our Editors' Choice Mophie Juice Pack Plus ($99, 4 stars), is a better bet. It will cost you more, but it will also extend your battery life threefold over the Reserve.