If you own more than one Apple handheld product on the list below, this is the extended battery you'll want to have, but mostly in case of an emergency.
A juice pack is an extended battery that you can attach to a handheld device to increase its battery life. For the case of the iPhone 3G, you definitely want one. Most juice packs, such as the Juice Pack Air, are designed for a specific model of the iPhone or iPod. The iPWR SuperPack is the first we've had our hands on that works with multiple models, including iPhone, iPhone 3G, iPod Touch (first and second generation), iPod Video, iPod Nano (third and fourth generation), and iPod Classic. Plus, the sub-$60 price tag makes it the most affordable and versatile juice pack on the market.
In order to support multiple devices, the iPWR SuperPack doesn't come in a form-fitting form factor. Instead, it's just a little square box that can be attached to the port at the bottom of the device. The box has the same width and depth as the iPhone and when used with one adds about 50 percent more length to it. It's not a good idea to keep it plugged in at all times, since the iPhone's port isn't the most sturdy of connections, but the phone can be used just fine with the pack attached.
Even if you don't mind the extra length, you will still need to remove the juice pack when you want to sync the device with a computer, or when you want to charge either of them. The JuicePack's USB port is located near the same space by which it attaches to the phone, making it impossible to connect it to anything else at the same time, so you'll need to bring the pack's USB cable and the iPhone's or iPod's USB cable when traveling. Other juice packs like the Mophie Juice Pack allow you to charge and sync the phone without having to take them off.
To its credit, the iPWR uses a standard Mini-USB port that can be found in the majority of handheld devices, so it won't be a problem if you happen to forget its USB cable. The included USB cable is retractable and compact to carry around. Also, the juice pack is equipped with a 1,800mAh battery that generally offers more juice than other packs of the same size that use lower mAh batteries.
We didn't feel the SuperPack's on/off switch served any purpose, since the only reason you'd want to attach the pack is when charging the device. Plus, the switch, too, is located in an obscure place, near the USB port, making it impossible to use while the pack is attached to a device.
When not attached to an iPhone or an iPod, the iPWR SuperPack has a top lid that covers its connector and USB port, which is useful for keeping dust out. Unfortunately, there is no convenient place to put the cover when the pack is attached to the phone. An option to clip the cover to the bottom of the pack would have been useful.
We tried the iPWR SuperPack with an iPhone 3G, and it brought the phone to a full charge (from completely dead) in about 2 hours. There is no battery gauge or indicator signifying how much juice is left in the pack, however. It only has a very bright green light-emitting diode (LED) that shuts off when the pack dies, or turns red after a full charge had been completed. The green light turned off when there was no more juice. Other than that, it stayed green all the time except when the pack was turned off or was being charged; then, it changed its color to red. The LED turned off again when the charging was completed.
The iPWR SuperPack is a compact, affordable, functional, and versatile extended battery. It's a good investment if you have multiple Apple handheld products, but it would be much more useful with a better port design and the addition of a battery gauge.