We spent more than 20 hours researching 160 USB battery packs, brought in almost 23kg of batteries, and tested them in a specialist lab in Canada all to find the best USB battery pack for any situation. Whether you need a pocketable pack to get through an evening out, a unit to leave in your bag to keep your device going for a busy day of meetings, or plenty of power for a week on the road, we've got you covered.
We know that when it comes to USB battery packs, someone who wants a pocketable model for topping off a phone only on occasion has different needs than a business traveller who wants to keep a tablet and two phones charged for back-to-back international flights. For each scenario, we set out to find the best balance of capacity, charging speed, size, and features. A hulking, heavy, cheap pack, for instance, isn't as good as a moderately priced one you'll actually use. We also looked for models that can cut down the clutter in your bag or pockets through the inclusion of convenience features such as multiple ports and integrated cables.
Once we established our test lineup, we worked with Cadex Electronics to put the packs through an exhaustive series of technical tests. We hooked up three samples of each model to Cadex's lab gear, getting insight into voltage curves, amperage, and how close the batteries' actual capacities came to matching what their makers claimed on the box. With the help of Cadex engineers, we sifted through and analysed all of that data and came up with solid recommendations for whatever amount of juice your power-hungry devices may need.
For a night out: The best pick for your pocket AmazonBasics Portable Power Bank with Micro USB Cable
If all you need is to get a few extra hours out of your phone, we recommend a credit-card-sized battery pack that's small enough to carry all the time and fits into even a slim pocket. For phones that use a Micro-USB connector (that is, most phones other than an iPhone), the AmazonBasics Portable Power Bank with Micro USB Cable 2,000 mAh is the best pack we've tested.
At less than $US10 ($13), it's the cheapest of the group we looked at, but it also has the highest tested capacity. Its built-in Micro-USB cord means one fewer cable to manage (and lose). The catch? You can purchase it only when you add it to a minimum $US25 ($33) order of items shipped by Amazon.
If you're an iPhone user seeking a pocketable model with a Lightning-type connector built in, the $US30 ($40) TravelCard is terrific; it also includes a built-in USB cable to recharge its battery. If offers just a bit less power than the AmazonBasics unit, but it's so much more expensive that it's worth the investment only if you can't accommodate our cheaper pick for purses or shoulder bags below.
For a day away: The best pick for your purse or shoulder bag EasyAcc 6000mAh Ultra Slim Power Bank
If you can make just a little more room in your pocket or bag, you can step up to a lot more power and a better value. The EasyAcc 6000mAh Ultra Slim Power Bank is about the size and thickness of an average smartphone, and it's the best-performing model in this class -- standing out thanks to its integrated cable and high-speed charging port.
In our tests, this EasyAcc model had the most available power, enough to fully charge a smartphone -- depending on size -- two or three times. You could even charge a tablet more than halfway from this unit's high-speed, 2.4-amp port.
For a longer trip: The best pick for a tablet plus a smartphone Anker PowerCore 15600
The Anker PowerCore 15600 is our pick if you need to charge a phone repeatedly or to keep a full-size tablet and phone topped up through a week of commuting or on an international flight. It's easily the most versatile of our picks, and it's inexpensive for its capacity.
In our testing, the PowerCore 15600 was a powerhouse: It had enough available juice to charge a smartphone five times or to fill a tablet almost twice. In fact, this model is even capable of providing a charge and a half to the massive battery on Apple's larger iPad Pro. And unlike other batteries in this group, both of its high-speed ports can provide power at 2.4 amps, simultaneously, handling tablets with the highest charging rate.
Its compact shape -- it resembles an eyeglasses case -- makes it easy to tuck away, but its 340.19g bulk could deter you from carrying it around all the time in a pocket or purse. With a briefcase, a laptop, a bag, a larger purse, or a backpack, it's a perfect match.
These picks may have been updated. To see the current recommendations, please read Wirecutter's guides.