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We’ve spent more than 140 hours testing 21 different battery cases (18 for the iPhone 6 and three for the iPhone 6 Plus), and we think the best battery case for most people is Anker’s Ultra Slim Extended Battery Case. It provides an above-average 117 percent of a full charge to the iPhone 6one full charge plus another 17 percentand at only $40, it’s by far the least expensive. The result is the highest ratio of charge percent per dollar and the lowest cost per full iPhone recharge out of all the models we looked at. It’s also the lightest and thinnest battery case we tested.
Why you might want a battery case
Depending on how you use your iPhone, draining its battery during an average day can be easy. If you rely on your phone to last a full day, and you don’t have the time (or physical access) to plop down next to a wall outlet, a battery casewhich puts a moderate-capacity rechargeable battery inside a bulky iPhone casecan be a smart choice. In the best circumstances, a battery case can double the battery life of your iPhone and then some. And unlike with stand-alone battery packs, you don’t need to bring a separate cable or figure out how to carry both devices together. You just slide or snap your iPhone into the battery case to get protection and power in a single unit. If you’re looking only for some protection, we can also recommend a regular case.
How we picked and tested
To test each battery case, we installed a fully drained iPhone 6 and set it to Airplane mode in the fully charged case. When the iPhone reached a 100 percent chargeor when it stopped chargingwe removed it from the case and drained the phone’s battery again. Assuming the battery case still had charge remaining, we then installed the phone in the case a second time, noting the phone’s battery percentage when the case stopped charging it. We recorded the charge percentages and times for each test, as well as the physical dimensions and weight of each battery case. We repeated each test a few days later and then once more for a total of three tests. We then averaged the charge results.
We also tested each case for subjective aspects of usability, such as how easily we could press the phone’s buttons and how the encased phone feels in the hand.
Additionally, we used a micro-USB cable to connect each battery case to a computer to test whether each case allows pass-through charging (the capability to charge the iPhone while it’s in the case) and data syncing.
Anker’s Ultra Slim Extended Battery Case is the iPhone 6 battery case with the best combination of good performance, price for the capacity, and least amount of additional bulk. It can provide 117 percent of a full charge to an iPhone 6, and its $40 price tag is crazy low for a battery case. Anker originally released the Ultra Slim at a higher price, but the price has dropped considerably, and the company has confirmed that $40 is the new “regular” price. The Ultra Slim offers the best charge value (2.9 percent of a full iPhone 6 charge per dollar, or $34.34 for a full charge) of any of the cases we tested by far. And it adds only 84 grams of weight, and just 6.1 millimeters of thickness.
When it comes to installation, most iPhone battery cases use either of two types of design: sliders or front frame. Anker’s Ultra Slim employs the slider design. You remove a short plastic cap at the top to slide the iPhone in place, and then reinstall the cap. Doing so is very easy compared with using the trickier front-frame design of Incipio, Odoyo, and some other cases, which requires you to remove a frame, install the iPhone in the base, and then snap the frame into place around the entire phone.