Editor’s note: This article is part of our roundup of USB-C battery packs.
USB battery packs designed to connect to the charging port of another device used to have limited capacity, offered slow charging while also recharging itself at a turtle’s pace, and cost and weighed a lot relative to the benefit they offered. Some larger-capacity batteries had advantages, but were typically designed to charge a laptop and only through a DC adapter or set of adapters.
The state of USB battery packs has improved noticeably over the last few years. With the very large scale manufacture of standard sizes of rechargeable lithium-ion battery cells, electronics makers have created affordable, high-capacity USB packs that range from recharging your iPhone 6s by about 50 percent up to the equivalent of a week’s worth of multiple full recharges of a set of iPads and iPhones.
Laptops used to be outside the range of USB battery packs, because laptops require so much juice to operate even in a low-power mode that an external pack couldn’t provide enough charge quickly enough over USB. The capacity of these older packs was small relative to weight, and they were expensive relative to capacity, too. Size and cost have dropped, but it took USB-C to solve moving electricity faster.
USB-C breaks through the wattage barrier by allowing much higher voltages and slightly higher amperages. (Wattage is the product of amps times volts, representing the total energy transferred.) This higher wattage allows a USB battery pack to recharge a 12-inch MacBook relatively speedy when put to sleep, although the units that I tested—save one—still can’t keep up with its power consumption while it’s active.
OS X should be updated to recognize that an external power source isn’t a power adapter, but rather a battery pack. Right now, recognizing it as a power adapter because it’s supplying charge doesn’t fiddle with settings enough to allow the typical 15W input to charge or maintain the battery state.
During my testing, in all cases except the MOS Go, I had to put my 2015 MacBook to sleep in order to charge it. Because USB-C can allow power to flow in either direction over a USB-C-to-USB-C cable, some packs require that you press a battery-level/wake button to start power flowing to a MacBook.
The iPad Pro can be charged quickly enough from an USB battery that they can be in use and charge simultaneously, however, as long as the output is over 10W (9.7 inch) or 12W (12.9 inch), the same wattage as the respective adapters that ship with the iPads. I tested all eight batteries with a 9.7-inch iPad Pro, and all except the Zerolemon ToughJuice managed to keep up.
USB-C’s higher rate of power flow also should let batteries recharge themselves more rapidly than with the limits of older USB standards, and yet none of the batteries tested really pushed the envelope. Most recharged at 10W or more slowly (5V at 2A), because they rely on a Micro-USB Type-A jack, limited to at most 5V at 2.4A. The Anker PowerCore+ 20100 managed closer to 12W over Micro-USB. While the Kanex uses USB-C for recharging, it’s limited to 12W as well.
Only the MOS Go takes advantage via its USB-C input and an appropriate adapter, such as ones from Google and Apple: it accepts nearly 30W of power and recharges in about two hours. Expect more battery packs in the future that have this faster charging—but also expect a premium. The MOS Go list price per mAh of capacity is almost three times that of the Anker PowerCore+ 20100.
The RavPower models support Qualcomm’s Quick Charge (QC) standards, which bump voltage way up. The older RavPower 20100 handles QC 2.0, and the newer Turbo refresh works with both QC 2.0 and 3.0, and can handle 24W (12V at 2A). Recharged with a RavPower QC2.0/3.0 30W charger (sold separately), the revised QC 3.0 RavPower managed only about 2/3rds of that rate, taking 4 1/2 hours to recharge its 74.3 watt-hour (Wh) total storage.
Being able to bring a relatively lightweight battery (from about half a pound to a pound and a half) that carries a partial MacBook charge to two full additional MacBook charges, or which could partly or fully recharge a MacBook and handle two to four iPhones and iPads simultaneously can make extended travel away from electricity very practical.
This can especially include long-haul flights where onboard power isn’t available or when that power isn’t enough to charge devices fully. For long and unexpected airport layovers, you could avoiding camping at an outlet or leaving hardware in a vulnerable place to charge via AC. You can also recharge a battery pack more quickly than several separate devices.
In general, if you deplete a battery and need to use it, give yourself a few hours to charge it to the 50 percent mark, and from two to five hours to recharge it fully. All lithium-ion and similar batteries charge most rapidly when they’re most depleted. The ZeroLemon TouchJuice is an outlier here: it has a 30,000 mAh battery, but only a 5V at 1A input port. That’s an estimated 11 hours to recharge it from empty without factoring in the slowdown as it nears being full.