Lenmar Helix Power Bank
According to Lenmar's curious zombie-themed marketing materials, the $100, 11000-mAh Helix 11000mAh Portable Power Pack (3.5 of 5 rating) can help you revive your dead portable devices, making them "undead." The Power Bank has four green "eyes" (really just status LEDs showing the remaining charge, but I'm playing along with the zombie theme here). The 4.7-by-3.1-by-0.9-inch battery weighs 9.1 ounces and sports three USB-charging ports: two 1.1A ports for charging phones, plus one 2.1A port for higher-draw devices such as the iPad. Unlike the iSound Portable Power, the Helix Power Bank can charge two phones and one iPad simultaneously.
You charge the Power Bank itself using the included Micro-USB cable. Plugged into Apple's 10W iPad USB charger, the Lenmar model took 6 hours, 49 minutes to reach its maximum charge. It then charged our dead fourth-generation iPad to 70 percent of full. Warning: Do not overcharge or drop the device, or the resulting zombie apocalypse will be your undoing.
Mophie Juice Pack Powerstation Duo
Like several other batteries here, Mophie's $100 Juice Pack Powerstation Duo (3 of 5 rating) can charge two devices at once. About the length and width of an iPhone 4, but twice as thick, the Powerstation Duo is the smallest and lightest charger of the group, measuring just 4.3 by 2.3 by 0.8 inches and weighing only 6.5 ounces.
The reason for this svelte size is that the Powerstation Duo has a capacity of merely 6000 mAh, and unsurprisingly it gave us the weakest charging result in this roundup: It restored our fully drained fourth-generation iPad's battery to just 39 percent before running out of power itself. On the bright side, charging the Powerstation Duo didn't take terribly long, requiring just 6 hours, 10 minutes using Apple's iPad USB power adapter.
Mophie Juice Pack Powerstation Pro
Mophie's $100 Powerstation Pro (3.5 of 5 rating) is the Powerstation Duo's bigger, tougher sibling. (Technically, it's the ruggedized version of the $80, non-Duo Powerstation.) The Pro comes clad in a shock-absorbing, thick-rubber bumper attached by six screws. Covering the sides, corners, and bottom, the bumper protects the battery's USB ports from shock and water. The bare top face of the battery shows four status LEDs along with the Mophie logo.
The case adds a bit of bulk—the Pro is slightly larger than the Duo, at 4.5 by 2.7 by 1.0 inches—but at just 7.1 ounces, this model is the second-lightest device we looked at. It has the same battery capacity as the Duo, at 6000 mAh, but it can charge only a single device at a time. The Pro charged itself quickly, taking 5 hours, 45 minutes to reach its full charge, and it charged our drained fourth-generation iPad back to 42 percent of full before running out of power itself. Unlike many of the other portable battery chargers, the Powerstation Pro has built-in overcharge protection.
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