Best Power Delivery 2.0 USB-C battery packs
With the growing availability of USB-C laptops, USB battery packs have hit the market. These packs can charge USB-C laptops at high speed while in use. When you’re out and about with one of these battery packs, you no longer have to worry about being tethered to a power adapter plugged into a wall socket.
We reviewed two 26,800 milliampere-hour (mAh) models, just shy of 100 watt-hours (Wh), from two well-known battery and accessory makers, RAVPower and Anker. Both batteries can output various combinations of voltages and amperages over USB-C, with a maximum of 30W, the same full-speed input wattage of a 12-inch MacBook. At 30W, a MacBook and 2016 or later MacBook Pro can be used and recharge its internal battery at the same time. Previous USB-C batteries maxed out at half that rate.
Power Delivery 2.0 USB-C battery packs: How we tested
I tested with a 2015 12-inch MacBook with a battery replaced several months ago by Apple that works at nearly full capacity. It took about 2 hours with the Anker and 2.5 hours with the RAVPower to charge the laptop from empty to full while it was active with about 50-percent brightness and occasionally going into sleep mode. That speed is about as fast as when plugged into the AC adapter shipped with the laptop by Apple.
The secret of these new batteries is support for the USB Power Delivery 2.0 specification, which allows a USB battery or AC adapter to negotiate with a mobile or laptop device for far higher wattages than the 15W (5 volts at 3 amps) maximum available from earlier USB-C batteries.
Because USB-C can pass power both in and out, both Anker and RAVPower allow recharging over that port, and that dramatically speeds up that task. Previous batteries I tested typically only allowed 12W or 15W recharging. The Anker recharges at up to 27W over USB-C, while the RAVPower works at 30W. That translates to about five hours to recharge instead of the 10 to 12 required by other USB-C batteries.
At higher wattages, we’ve consistently seen more efficient power transfer, allowing more of a battery’s capacity to be available relative to what’s lost in heat and power conversion. Both the batteries tested perform substantially better than their 20,100 mAh (about 70Wh) USB-C predecessors, extracting 30 to 100 percent more usable power. That gives you more bang for the buck and more bang for the ounce. That’s especially critical for the RAVPower, which has terrible performance in its 20,100 mAh model.
After charging the MacBook, both batteries had about 50 percent charge remaining. The 2017 15-inch MacBook Pro models have just under twice the battery capacity of the MacBook, allowing for more than a full recharge of those bigger laptops, too, although you may not be able to do more than maintain the current charge level while it’s in active use. The 13-inch MacBook Pros with batteries in the middle range should recharge while you work.
Power Delivery 2.0 USB-C battery packs: Charging rates
If you’re doing the math on all of the above, you might notice that dividing watt-hours by hours doesn’t result in a perfect match for charging and recharging. That’s because to avoid overcharging and damaging battery cells, the internal circuitry in all lithium-ion battery systems slows charging as it approaches nominally full capacity. It also doesn’t charge the internal cells to the rated total for the same reason. Using a USB-C battery monitoring device, I could see amperage drop from nearly 2A to 1A after the MacBook reached a 90 percent internal charge, and then to about half an amp as it got even closer to full.
The converse is also true: you’ll see substantially faster charging and recharging when the battery pack or the Mac battery is closer to empty, making it fast to top up one of these batteries’ cells on a flight layover where you can plug into AC, or quickly transferring charge to a Mac if it’s running towards empty. (Batteries between 100Wh and 160Wh are subject to airline approval and carry-on limits, which is why both these are under 100Wh.)
Interestingly, both batteries can be recharged from a MacBook, as well as any USB-C energy source. You may need to press the power button on each if you see it drawing charge (the LEDs lighting up one at a time in sequence) rather than providing charge (macOS showing a charger attached and solid lights on the packs).
Look in each review for more specifics about each battery pack’s strength and weaknesses.