It takes a lot of power to light up an iPad's 9.7-inch screen—and even more to power the fourth-generation model's Retina display. That's why the device is packed full of battery capacity—an impressive 11,560 milliampere hours' worth for the latest model. But although our battery tests have shown that, under heavy use, the fourth-generation iPad can last for more than 9 hours on a single charge, sometimes you need even more juice.
Whether you're exploring the great outdoors or enduring a power outage, a portable charging device—that is, a big battery—can come in handy when electrical outlets are either unavailable or, as is often the case, not functioning. Portable batteries can also charge your smartphones, media players, and other mobile gear that charge over USB.
We recently put nine such devices through their paces and found that while all could help in a pinch, only one could provide a full recharge of a fourth-generation iPad.
What to look for
You should keep an eye out for several things when you're shopping for a portable charging device, including capacity, convenience, and cost. If you're seeking a portable charger that offers the greatest amount of juice for your iPhone, iPad, or other USB-charged device, look first at battery capacity, measured in milliampere-hours. The batteries we tested range from 6000 mAh to 16,000 mAh.
The downside is that higher-capacity batteries are generally larger and heavier than lower-capacity models. If you're packing light, adding a 1-pound charger to your bag may not be wise. Similarly, the higher capacity a portable battery has, the longer the battery itself takes to charge: Some need as long as 14 hours, requiring you to leave them plugged in all night.
Many portable batteries can charge over a Micro-USB cable, eliminating the need to pack another power supply. (They'll charge more quickly with your iPad's power adapter, or another dedicated USB charger, than with a computer's USB port, but either will work.) Some, however, require a particular AC adapter, which is less convenient. A few have AC plugs built in, so you need nothing but an electrical outlet to fill them up.
iSound Portable Power
Despite the name of its vendor, iSound, the $90 Portable Power (3 of 5 rating) does not have built-in speakers. But with a battery capacity of 8000 mAh, the iSound Portable Power offers a good amount of charging power; and with five USB ports, it can accommodate more devices than most of the other batteries we tested. At 3.5 by 3.3 by 1.0 inches, the 8.2-ounce, squarish Portable Power is almost identical in size to Apple's older 85W MacBook Pro power adapters.
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