Blue light has a dark side
Exposure to blue light at night, emitted by electronics and energy-efficient lightbulbs, can be harmful to your health.
Until the advent of artificial lighting, the sun was the major source of lighting, and people spent their evenings in (relative) darkness. Now, in much of the world, evenings are illuminated, and we take our easy access to all those lumens pretty much for granted.
But we may be paying a price for basking in all that light. At night, light throws the body's biological clock—the circadian rhythm—out of whack. Sleep suffers. Worse, research shows that it may contribute to the causation of cancer, diabetes, heart disease, and obesity.
But not all colors of light have the same effect. Blue wavelengths—which are beneficial during daylight hours because they boost attention, reaction times, and mood—seem to be the most disruptive at night. And the proliferation of electronics with screens, as well as energy-efficient lighting, is increasing our exposure to blue wavelengths, especially after sundown.
Daily rhythms influenced by light
Everyone has slightly different circadian rhythms, but the average length is 24 and one-quarter hours. The circadian rhythm of people who stay up late is slightly longer, while the rhythms of earlier birds fall short of 24 hours. Dr. Charles Czeisler of Harvard Medical School showed, in 1981, that daylight keeps a person's internal clock aligned with the environment.
The health risks of nighttime light
Some studies suggest a link between exposure to light at night, such as working the night shift, to some types of cancer, diabetes, heart disease, and obesity. That's not proof that nighttime light exposure cau nor is it clear why it could be bad for us. But we do know that exposure to light suppresses the secretion of melatonin, a hormone that influences circadian rhythms, and there's some experimental evidence (it's very preliminary) that lower melatonin levels might explain the association with cancer.
A Harvard study shed a little bit of light on the possible connection to diabetes and possibly obesity. The researchers put 10 people on a schedule that gradually shifted the timing of their circadian rhythms. Their blood sugar levels increased, throwing them into a prediabetic state, and levels of leptin, a hormone that leaves people feeling full after a meal, went down.
Even dim light can interfere with a person's circadian rhythm and melatonin secretion. A mere eight lux—a level of brightness exceeded by most table lamps and about twice that of a night light—has an effect, notes Stephen Lockley, a Harvard sleep researcher. Light at night is part of the reason so many people don't get , says Lockley, and researchers have linked short sleep to increased risk for depression, as well as diabetes and cardiovascular problems.
The power of the blues
While light of any kind can suppress the secretion of melatonin, blue light at night does so more powerfully. Harvard researchers and their colleagues conducted an experiment comparing the effects of 6.5 hours of exposure to blue light to exposure to green light of comparable brightness. The blue light suppressed melatonin for about twice as long as the green light and shifted circadian rhythms by twice as much (3 hours vs. 1.5 hours).
In another study of blue light, researchers at the University of Toronto compared the melatonin levels of people exposed to bright indoor light who were wearing blue-light–blocking goggles to people exposed to regular dim light without wearing goggles. The fact that the levels of the hormone were about the same in the two groups strengthens the hypothesis that blue light is a potent suppressor of melatonin. It also suggests that shift workers and night owls could perhaps protect themselves if they wore eyewear that blocks blue light. Inexpensive sunglasses with orange-tinted lenses block blue light, but they also block other colors, so they're not suitable for use indoors at night. Glasses that block out only blue light can cost up to $80.
Less-blue light
If blue light does have adverse health effects, then environmental concerns, and the quest for energy-efficient lighting, could be at odds with personal health. Those curlicue compact fluorescent lightbulbs and LED lights are much more energy-efficient than the old-fashioned incandescent lightbulbs we grew up with. But they also tend to produce more blue light.
The physics of fluorescent lights can't be changed, but coatings inside the bulbs can be so they produce a warmer, less blue light. LED lights are more efficient than fluorescent lights, but they also produce a fair amount of light in the blue spectrum. Richard Hansler, a light researcher at John Carroll University in Cleveland, notes that ordinary incandescent lights also produce some blue light, although less than most fluorescent lightbulbs.
What you can do
Use dim red lights for night lights. Red light has the least power to shift circadian rhythm and suppress melatonin.
Avoid looking at bright screens beginning two to three hours before bed.
If you work a night shift or use a lot of electronic devices at night, consider wearing blue-blocking glasses or installing an app that filters the blue/green wavelength at night.
Expose yourself to lots of bright light during the day, which will boost your ability to sleep at night, as well as your mood and alertness during daylight.
image: (C) Innovatedcaptures | Dreamstime.com
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First Name (Optional)The Best USB Battery Packs and Power Banks: Reviews by Wirecutter | A New York Times Company
Your guide
Mark Smirniotis
Over the past two years, we’ve considered nearly 300 USB battery packs (also known as power banks) and spent hundreds of hours testing more than 40 of them to find the ones that offer the best value and reliably keep gear charged. The credit-card-sized
has consistently been our go-to battery to give a smartphone a partial charge to make it through the day. The
is just a little bigger and provides one to two full smartphone charges, and it has convenient built-in cables. Our larger pick, the , can charge your phone every day for a week or keep a fleet of devices going for shorter stints. And for Android devices that are Quick Charge–capable, we found that the medium-size
will provide really fast Quick Charge 3.0 speeds at a good price. (If you already have a device with a USB-C port, you’ll get the fastest charging and future-proof tech from dedicated
This is still the most reliable credit-card-sized battery, and a staff favorite years after we first recommended it. The TravelCard can give a smartphone like an iPhone 7 or Galaxy S8 about half a full charge, it’s only 5 mm thick, and it has an integrated Lightning or Micro-USB cable.
The integrated Micro-USB and Lightning-connector cables make it convenient to carry every day, for every device. The aluminum body is the size of a bar of soap, and the Bolt has enough power to charge a midsize smartphone twice.
*At the time of publishing, the price was $27.
The Anker PowerCore 20100 has enough power to recharge a tablet and two smartphones on a long flight, or a smartphone a day for nearly a week. It’s about the size of two decks of cards lined up end to end.
*At the time of publishing, the price was $42.
The Presto is the best one-size-fits-all battery pack if your Android device supports QC 3.0 and you need faster charging. It’s about the size of most midsize smartphones, but it has enough capacity to recharge such a phone about three times.
*At the time of publishing, the price was $21.
These are our top picks, but we have a few runners-up in the size-specific sections below.
Expand all
Wirecutter has been researching and testing battery packs for more than four years, and I’ve been working on this particular guide for nearly two of them. I’ve lost track of the absurd number of hours I’ve spent reading about, testing, and using the roughly 300 battery packs I’ve cataloged over the years. On top of that, I’ve covered various other power devices for Wirecutter, and I’ve talked to engineers, safety experts, and the companies behind uninterruptible power supplies, solar chargers, and surge protectors. Oh, and more batteries, too.
When we need a little extra expertise, we call on Lee Johnson, an electrical engineer in Littleton, Colorado. For a previous update to this guide, we even visited with the Vancouver-based battery-analysis specialists at
to come up with our picks (which we shared with the
audience).
We think the best way to shop for a USB battery pack is to consider three factors:
the device(s) you need to charge
how many times you need to be able to charge your devices while on the go
how much bulk and weight you can tolerate carrying around
Someone who wants a pocketable model to occasionally extend the use of a dying phone has different needs than a business traveler who needs to keep a tablet and phone charged for back-to-back international flights.
Our five favorite batteries plus a 3-by-3-inch sticky note for scale.
Photo: Kyle Fitzgerald
With these factors in mind, we have divided power banks into three main categories: the slimmest, ; convenient, and larger battery packs with more power for . (Because of price premiums and compatibility issues, we have a separate pick for , a feature that lets some Android devices charge faster than normally possible with USB.) This approach lets us narrow down the hundreds of batteries for sale to just the most useful designs.
Capabilities
Weight and size
Price range
Boost a dying phone to get through the day
Less than 3 ounces, credit card or lipstick tube shape
$30 and up
Everyday carry
Fully charge a smartphone one or two times
Less than 8 ounces, the size of a deck of cards or a bar of soap
$30 to $40
More power
Charge a smartphone every night for a week, or a tablet a couple of times
Up to a pound, the size of a portable hard drive
$40 to $50
Because battery capacity is an essential measurement for this guide, we talk a lot about milliamp-hours (mAh) and milliwatt-hours (mWh), or just watt-hours (Wh). You don’t need to know the nitty-gritty of electrical engineering, just that these units of energy are measurements of capacity, like liters or gallons in a fuel tank. (The figure mAh is the one you’ll see most frequently on a spec sheet, though .)
To give you an idea of the scale of these capacities, though, we put together a list of the battery capacities of some common devices. (If your device isn’t on the list, you can usually find its battery capacity with a quick Google search, or you can just estimate what you’ll need based on a similarly sized device on the list.)
Piles of drained batteries frequently overwhelm our desks.
Photo: Kyle Fitzgerald
Over the course of researching the previous two major updates to this guide, we cataloged 252 different batteries in a ridiculous we’re now up to nearly 300 batteries total. Once we find the most promising batteries on paper, we get samples of each and put them through a battery of tests (ha, a battery of tests—this stuff just writes itself!) to find out how fast they charge smartphones and other devices, how quickly they can recharge themselves, and how close their real-world capacities are to what’s advertised on the box. As of this update, we’ve gone hands-on with nearly 50 battery models, from manufacturers large and small.
To whittle down the hundreds of batteries for sale to a manageable few dozen for testing, we dismiss units with obvious flaws—mainly those power banks that charge either your device or themselves more slowly than similarly priced models. For smaller packs meant to be carried every day, we favor models that have built-in cables. Having a built-in Lightning or Micro-USB cable (or even better, both) can make it easier to carry a power bank in your pocket or small bag without having to bring along a tangled-up cord. The combination of integrated cables, plus a standard USB-A port for plugging in longer or specialty cables, is the most flexible arrangement.
That process still leaves us with dozens of models, so we compare those batteries on the basis of a few quick calculations:
capacity for the given price (mAh/$)
weight for the given capacity (ounce/mAh)
volume for the given capacity (cubic inch/mAh)
These calculations can help us find a few outliers, but honestly, batteries are starting to look more and more similar as manufacturers hit the limits of current technologies. Some brands consistently sell reliable batteries at a fair price, while others focus on flashier designs and packaging in order to charge a premium, but underneath, there’s little difference. So we also take into account availability and warranty coverage, since a recommendation from us will do you no good if you can’t purchase the item or if a company won’t replace a battery that fails due to manufacturing defects.
Cadex devoted a corner of its lab to test almost 20 models—nearly 60 batteries in all—for us in 2015.
For our most recent update, we tested our top contenders using a combination of USB ammeters and variable resistive loads. Because battery capacity actually , we tested every battery at a constant output—specifically, 1 amp. This amount is lower than what most recent devices draw—and this choice may result in slightly higher capacity ratings than you’ll see in the real world—but doing our tests this way gives us apples-to-apples data points. If one pack’s maximum output is 1.5 A and another is 2 A, for example, testing them at the maximum discharge won’t give us a fair comparison of the capacity of the underlying battery cells.
Pull QuoteIf you’re trying to estimate your needs, expect to get less from the source battery than its manufacturer claims, and expect your device to use more than its own battery capacity when charging.
Aside from the voltage considerations in battery capacities, it’s also important to note that manufacturers advertise laboratory-perfect capacity numbers. In reality, no battery or charger is perfectly efficient, so we always expect to lose a few percent here and there in testing. If you’re trying to estimate your needs, expect to get less from the source battery than its manufacturer claims, and expect your device to use more than its own battery capacity when charging.
Related to this topic, while most vendors advertise a battery’s capacity in milliamp-hours, or mAh, we also list capacities in watt-hours (Wh). It’s just a simple conversion, but one that makes it easier to compare the capacities of batteries across different types of technology. Because power (in watts) equals amps multiplied by volts (A × V = W), two batteries with the same mAh listing could have different real-world capacities. With so many different battery-based devices, listing watt-hours in our guides makes it easier to directly compare different types of products. If you’re curious to learn more,
about why you’ll see both watt-hour (Wh) and amp-hour (Ah) numbers in more of our guides going forward.
We use a variety of highly sophisticated doodads and whatsits for battery testing.
Photo: Mark Smirniotis
We also test the maximum output, or charging speed, of each port individually. Large phones and tablets draw more power, faster, than smaller devices, and that speed is measured in amps (A). Once upon a time, our MP3 players all charged with 0.5 A from a computer’s USB port, but it would take forever to charge a modern device that way, so speeds have steadily increased to almost 3 A for some devices. But both sides—charger and device—must support faster charging: If your device wants 2.5 A, but your battery can supply only 1 A, the lower limit wins.
In our latest round of tests, using our variable loads and an ammeter, we checked each port by slowly increasing the discharge rate until the battery cried uncle: USB power is supposed to be 5 V with a 5 percent margin, so we considered a port’s maximum output to be the current it could supply without dropping below 4.75 V (or without protection circuits shutting the battery down). Some packs can fast-charge on only one port at a time, throttling back charging on additional devices you connect, so once we knew the individual port maximums, we also tested each device to determine its simultaneous maximum output across all the ports.
(In the smallest category of batteries, we forgave slow charging, because high-amperage circuitry requires more room and sophistication than low-amperage modules. But we otherwise insisted on charging capabilities better than 2 A to keep up with iPads, other tablets, and recent smartphones, and you should, too.)
Finally, we considered the size, shape, features, and build quality of each unit, along with minor elements such as the style and usefulness of the LED gauge or the finish on the plastic. Of course, price is always a factor, but because the street price of these batteries can vary so much—sometimes by $5 to $10 over the span of a few weeks—we didn’t give much weight to small pricing differences.
The TravelCard has been the most reliable of the credit-card-size batteries we’ve tested, but it’s worth buying only if you absolutely need the small size.
Photo: Kyle Fitzgerald
This is still the most reliable credit-card-sized battery, and a staff favorite years after we first recommended it. The TravelCard can give a smartphone like an iPhone 7 or Galaxy S8 about half a full charge, it’s only 5 mm thick, and it has an integrated Lightning or Micro-USB cable.
If you need the absolute smallest battery to keep your phone going through the end of the day when you can’t get to an outlet, the
is the most convenient and reliable option. A little longer and wider than a credit card, and roughly three times as thick, the TravelCard stands out from other small batteries because it has two integrated cables: one with a standard USB-A plug to recharge the battery itself, and one with either a Micro-USB or Lightning-connector plug (depending on which TravelCard version you buy) to charge your device. Because you don’t need to carry any cables, there’s nothing extra to forget, and the TravelCard is always ready to go. It’s light and well-made, with cables that fit securely without jamming or falling out—a real problem with some of the cheapest credit-card-size batteries. Since this model’s announcement in 2014, several Wirecutter staffers have been personally using the TravelCard with positive results.
Though almost as thin as the Travelcard, the Flux charger gets its extra capacity by being longer and wider.
That said, even the best batteries at this size have limitations. To preserve battery longevity and avoid heat buildup, they’re limited to relatively slow input and output charge speeds. The TravelCard is similar to competitors here, discharging and recharging at about 1 amp. The LithiumCard from LinearFlux is the only standout of the small batteries we’ve tested, able to put out up to 2 A, closer to batteries in the larger categories. But the LithiumCard has about 20 percent less capacity than our pick, and since you’ll likely be using your phone while charging it with something this size, faster charging speed isn’t the top priority.
Dollar for dollar, the capacities of packs this small are as unimpressive as the charging speeds. The TravelCard averaged 1,048 mAh (3.8 Wh) while that’s enough capacity for it to add 30 to 50 percent of a full charge to most smartphones, it pales in comparison to our top pick in the everyday-use category, which offers five times the capacity for a lower price. Even among credit-card-size batteries, some models eke out a few more mAh than the TravelCard. For example, the
provided only about 70 percent of its promised capacity, but that’s still double the capacity of the TravelCard. (That said, the Flux is closer in size to an index card than a credit card, so it’s not as pocketable as the TravelCard and is much less capable than , which is thicker but narrower.) The , similar in size and price to the TravelCard, provided a slightly higher capacity as well, but the TravelCard is still the better choice because of its integrated USB cable for charging itself: An extra 100 mAh probably won’t make a huge difference in how you use a battery, but never needing an extra cable is more than just a convenience—it’s a relief.
The Bolt is a bit smaller and a little thicker than most smartphones—overall, it’s a good size to carry every day.
Photo: MIchael Hession
The integrated Micro-USB and Lightning-connector cables make it convenient to carry every day, for every device. The aluminum body is the size of a bar of soap, and the Bolt has enough power to charge a midsize smartphone twice.
*At the time of publishing, the price was $27.
If you can make just a little more room in your pocket or bag, the
packs a lot of value into a battery the size of a bar of soap. The Bolt was the only model we tested that hit every item on our wishlist: fast output, three different ways to charge devices, sturdy materials, and enough capacity to charge most smartphones twice over. Though it’s a few dollars more than many batteries this size, you get more for that extra money.
The Bolt didn’t hold the most energy, but its other features make it more convenient.
The Jackery Bolt (left) has built-in Micro-USB and Lightning cables so you don’t need anything else on the go. The Anker Fusion (right) has a built-in power plug, which means you don’t need a wall charger but you still need to bring cables with you.
Photo: Kyle Fitzgerald
Pull QuoteThe Jackery Bolt was the only model we tested that hit every item on our wishlist: fast output, three different ways to charge devices, sturdy materials, and enough capacity to charge most phones twice over.
We’re big fans of having an integrated device cable on an everyday battery pack—when running out the door with a pile of batteries to choose from, we’ll take the one with built-in cables every time. But many companies sell one version with a Micro-USB plug and a different version with a Lightning-connector plug, making you choose which one to buy. Even if you get the “right” one, a Lightning-only pack can leave you stuck when you need to charge a device other than an iPhone (say, a camera, e-reader, tablet, or Bluetooth headphones), while a Micro-USB version won’t charge Apple devices. With both cables on the Bolt, you truly have nothing extra to bring along.
The Jackery Bolt is small enough to carry in any bag and fits comfortably in most jacket, sweatshirt, or large pants pockets.
Photo: Michael Hession
The Bolt’s maximum combined output is 2.7 A, and it has a standard USB port that can put out all of that at once—it offers the fastest speed of any small pack we tested—so you have the option of using longer or svelter cables if necessary. Cable size matters, and the chunky cables on the Bolt might cause problems if you use tight cases on your devices. If you do, or if you’ll never need a Lightning cable, our
might be the right choice for you.
The Bolt has enough capacity to charge small smartphones twice and larger models at least once. In our tests, it averaged 20.06 Wh (3.99 Ah) of discharged capacity at a 1 A rate. The more expensive Goal Zero Flip 30 beat it handily, with 25.55 Wh (5.20 Ah), but in addition to the higher price, the Flip 30 lacks the integrated device cables that make our picks so convenient.
The biggest downside to the Bolt is the thickness of the housing around the connectors. Though nice and sturdy, the connectors are too bulky to work with cases that have a small opening for the charging port. For example, none of the integrated-cable packs we tried would work with the
case we had on an iPhone 6s. During testing, we also noticed that while the Bolt is itself pocketable, the length and orientation of its charging cables make it difficult to slip in your pocket while charging your phone—the battery’s longer dimension ends up positioned perpendicular to the phone’s.
The EasyAcc is slimmer than our top pick, but you have to choose between an integrated Lightning cable or a Micro-USB cable—you can’t have both.
Photo: Michael Hession
Roughly the size and shape of a smartphone, EasyAcc’s power bank has either a built-in Micro-USB cable or, for a few dollars more, a built-in Lightning-connector cable. The Lightning version charges iPhones more slowly than our top pick but is otherwise similar in price and capacity.
was our previous pick in this category, and it’s still a great pack if you need only one type of built-in charging cable instead of the two that the Bolt offers, or if you just want a slimmer profile. This EasyAcc model is the size, shape, and weight of a medium-size smartphone, compared with the Bolt’s more portly figure, which is akin to a small bar of soap. While other companies offer batteries with similar dimensions, the EasyAcc’s built-in charging cable and impressive capacity for the price make it one of the best values in this category.
The EasyAcc is about the size and shape of a midsize smartphone, so if your pocket can hold your phone, it could hold this battery instead.
Photo: Michael Hession
The EasyAcc is available with either a
or—for $5 more—a . The cable on the Micro-USB version maxes out at 2 A charging, but the one on the Lightning-connector version chugs along at only 1 A. Since you can keep your phone plugged in while you use it, slow charging isn’t a dealbreaker for an otherwise handy battery, but it is slow enough that we’d disqualify the Lightning-connector model if it were a cable-less pack. And if you’re using the secondary USB-A port and your own cable for charging, you won’t have a problem charging at higher speeds: Though the port is marked for 2 A, we had no trouble pulling over 2.4 A in our tests. Overall, the EasyAcc is a serious contender for anyone without Apple devices, and even some iPhone owners might be willing to put up with its slower charging speeds if they prefer its thinner, more pocket-friendly design compared with the Jackery Bolt. Still, the Jackery Bolt’s charging options and speed make it a better choice for most people.
The PowerCore 20100 can charge two standard USB devices as fast as possible simultaneously, and has the capacity to do so a handful of times.
Photo: Kyle FItzgerald
The Anker PowerCore 20100 has enough power to recharge a tablet and two smartphones on a long flight, or a smartphone a day for nearly a week. It’s about the size of two decks of cards lined up end to end.
*At the time of publishing, the price was $42.
is the best value for anyone who needs more power than our everyday picks offer and doesn’t need to fit their battery into a pocket or a small bag. With 74 Wh (20,000 mAh) of capacity, this Anker pack can charge your smartphone every day for a weeklong work trip or keep two devices charged for a long weekend away. It’s also a few ounces lighter than our last large pick—the RAVPower 22000—and about 20 percent smaller, yet it still has 90 percent of the capacity of the older, larger pick.
When we tested the output on the PowerCore 20100, we found that it was able to charge two devices at full speed—just over 2.4 A—without any problems. Some power banks, including the smaller , can charge at full speed from either of their two ports, but not both. The best batteries, like the PowerCore 20100, can charge on every port at once without slowing down. That makes this model more versatile when you have multiple devices, which is likely if you’re bringing a bigger battery like this on a plane trip or some other long journey.
Bigger packs with three or four ports are available, but they come at a pretty big price premium. Plus, those packs are much bigger and tend to weigh more than a pound. Our pick, at about 12.5 ounces, has plenty of power for most situations but is still small enough and light enough to tote in a day pack if you’re out touring a city.
Pull QuoteThe best batteries, like the PowerCore 20100, can charge on every port at once without slowing down.
When it comes time to recharge the battery itself, a big pack like the PowerCore 20100 needs to be left overnight. We found the recharge speed was in line with Anker’s 2 A rating, but that meant it was roughly 10.5 hours before the power bank reported as full and we had measured 97.2 Wh into it. This is pretty standard for large packs, and is a limitation of USB power in general. Newer
can overcome this problem, as can our
if you have compatible chargers and phones, but those are still niche items for a lot of people. To tackle this limitation, Anker and others have started to experiment with power banks that have two recharging ports meant to be used simultaneously. The
are roughly the price and capacity of our pick but can recharge twice as fast via two Micro-USB inputs. Though the new design is a clever solution, these battery packs won’t save most people that much charging time—not , that is.
Anker has built a reputation for quality, and stands behind it. This accessory company is one of the very few to offer phone support during business hours in addition to email support. If you do have any problems, Anker includes an 18-month warranty and even covers return shipping on your item.
Photo: Kyle Fitzgerald
The Presto is the best one-size-fits-all battery pack if your Android device supports QC 3.0 and you need faster charging. It’s about the size of most midsize smartphones, but it has enough capacity to recharge such a phone about three times.
*At the time of publishing, the price was $21.
If you’re looking for a power bank capable of charging your
Android device, the
is the best all-around battery pack available. It can charge most smartphones about three times, has an extra port for charging a second device, and recharges itself at the faster QC 3.0 speeds. Though our other picks provide useful extras like integrated charging cables, as well as more value when it comes to capacity per dollar, a Quick Charge 3.0 power bank like the Presto 10000 PBT10 can charge a compatible device from zero to 70 percent in about 30 minutes.
The Presto 10000 PBT10 is smaller and lighter than the first power banks available with Quick Charge 3.0 in 2016, including the larger , our previous pick (since replaced by the , which has the same dimensions). Anker’s battery is still a good choice if you need the massive capacity, but the Presto 10000 PBT10 is about 65 percent the size and much easier to carry every day—it’s about the size and shape of a midsize smartphone.
both make packs that are competitive with our pick, but both are shorter and thicker, so it’s harder to slide them into a tight pocket as most people are bound to do at some point with an everyday power bank.
Despite the slim shape of the Presto 10000 PBT10, it offers two charging ports—other models we tested have just one. Only one of the ports is capable of QC 3.0 speeds (easily identified by the green plastic), while the other one charges at the standard USB full speed of 2.4 A. In our tests, both ports could charge devices simultaneously without one limiting the output of the other.
Compared with our previous Quick Charge pick from Anker (left), the Tronsmart Presto 10000 PBT10 (right) is slimmer and shorter, and fits alongside a smartphone much better.
Photo: Kyle Fitzgerald
The best Quick Charge power banks also recharge with the faster QC 3.0 standard using traditional Micro-USB cables, and all three of the top packs we tested did just that. We clocked the Tronsmart Presto 10000 PBT10 as recharging at 17 W, compared with the 18 W maximum, when it started from empty. But all the packs we tried were significantly slower when charging from a non-QC power source. The Presto charged at just 7.5 W, though that’s the same as the pack from Anker and faster than the Aukey pack (less than 4 W). If you’re going to use a Quick Charge pack like this, be sure to use a Quick Charge power source or you’ll be waiting a long time. (We don’t currently have picks for Quick Charge 3.0 wall chargers, but
both make compatible versions of our favorite single- and multi-port chargers.)
Green USB ports indicate QC 3.0 capability. These ports will charge compatible Android devices much faster than standard USB-A ports, and other devices a bit more slowly.
Photo: Kyle Fitzgerald
Tronsmart’s power bank did slightly better than the competition when we tested the available capacity too. Over three discharges, the pack averaged about 35.2 Wh (9,500 mAh), nearly 98 percent of the promised capacity. That’s a big jump from discharge averages in the mid–80 percent range for the competition and represents an extra quarter of a charge for most smartphones. While numbers in the 80s are common and not worth dismissal by themselves, when battery packs like the Presto 10000 PBT10 discharge nearly their whole capacity in testing, we consider it exceptional.
Anker is well-known for excellent customer support, via email or phone. While researching the Tronsmart, we anonymously contacted that company’s email-only support with a problem to test response time. A representative responded five hours later with some troubleshooting tips, plus instructions for how to initiate an exchange if we couldn’t resolve our problem. While phone support is always a plus, Tronsmart’s prompt and detailed email support left us feeling confident in our pick.
An important note for anyone taking USB batteries on flights: The
passengers to bring spare batteries in carry-on bags, but not in checked luggage. (If you need to gate-check a planned carry-on bag, you are legally required to shift any lithium-ion batteries from that bag to your actual carry-on.) There is no limit to the number of batteries you can carry for personal use, so long as each has a capacity of 100 watt-hours or less. All the batteries we reviewed for this guide have capacities that fall beneath the threshold.
For your pocket
sells for about the same price as our top pick, the TravelCard. Both offer the choice of an integrated Micro-USB or Lightning cable for charging your device, and both are about the same size and weight. But the TravelCard also has a short USB cable to recharge itself. That’s a feature the Slim Boost lacks, so you’ll need to carry an extra Micro-USB cable to recharge it, which is less than ideal for a power bank built for portability and convenience. And though they both charge devices at a similar speed, the Slim Boost had up to 35 percent less available capacity than the TravelCard in our tests.
discharged an average of 9.77 Wh (2.05 Ah) in our tests, which was lower than its advertised 14.4 Wh but still better than the results from our top pick. However, the Flux is larger than our top pick from TravelCard, and that’s a key point for a battery meant to be carried in the smallest of pockets or wallets.
For everyday use
While some batteries have integrated cables,
has an integrated wall charger. The Fusion is roughly the price and volume of the Jackery Bolt, with only a slightly smaller capacity. Though the Fusion performed as advertised in all our tests, its built-in charger isn’t as compelling for most people as the Jackery’s design. The Fusion’s shape and size—a 3-by-3-inch square about an inch thick—isn’t pocket-friendly, and it lacks the higher capacity of big packs that commonly live in backpacks or luggage. And although every device, every time, needs a cable to charge from a power bank, you need a wall charger only sometimes. With the Fusion, you get the extra bulk of the integrated wall charger, and you still have to carry cables, too.
is as pocketable as a smartphone—that is, perfect for some, and still too big for many—at around a third of an inch thick. But it’s about the same width, and just a hair shorter, than the
we recommend after the Jackery Bolt. The EasyAcc offers more capacity, the ability to charge two devices at once, and an integrated cable for a lower price than the PowerCore Slim.
Goal Zero’s new
is about the same overall size as our top everyday pick—just closer to a fat deck of cards than a long bar of soap. Its price is around 25 to 30 percent higher than that of our top pick, roughly proportional to the Flip 30’s higher tested capacity of 25.55 Wh (5.2 Ah). But instead of an integrated cable to charge your device, the Flip 30 offers a standard USB port, so you need to remember to bring a cable along. The Flip 30 recharges itself at 2 A through a small USB plug that flips out and can plug into a standard USB-A port. While the flip-out plug is nifty, plugging it into most chargers isn’t easy: The battery tends to block other ports, and it has to balance precariously when you charge it from a wall outlet or charger.
We tried to test , which comes with a Lightning cable, but the Micro-USB power-input port (for charging the battery itself) was poorly aligned with the battery’s shell, and the port broke loose from the housing when we tried to remove the charging cable.
For more power
are slightly thicker and heavier versions of the power bank we recommend. For a slightly higher price, the Elite 20000 and the 26800 incorporate a second Micro-USB input port, allowing you to recharge them with two cables simultaneously. But you need —a charger isn’t provided—and if you’re traveling with one of these packs, you must bring two cables, too. However, they have three output ports with a combined maximum output of 6 A that can charge three devices at about 80 percent of full speed. If we needed a three-output battery, and if we didn’t mind the extra bulk, and if we had a dual charger already, we’d certainly consider getting either of these power banks, but that’s too many “ifs” for us to recommend them for most people. Like , the
has only one input port, but we still prefer our pick because it’s slightly smaller and lighter.
Though the
had solid output in our tests—2.4 A on any of the USB ports, with a combined max of 4.6 A in testing—its recharging was noticeably slower than that of our pick: It never pulled more than 1.4 A, compared with 2 A maximum for the Anker PowerCore 20100. At just 75 percent as fast as our pick, the Brilliant would take a few extra hours to fill up.
We were ready to recommend the
as a budget pick: Even though it has a lower capacity than any other pack in this size category, its price is so low that it’s an impressive value overall. Combine that value with high-power input charging, one high-power output port, and a QC 2.0 port for compatible devices, and this battery is a good choice for anyone on a budget who needs only two or three phone charges. But this model went on backorder while we were testing, and the alternative models from Monoprice all have drawbacks, such as fewer ports or slow charging, that keep us from recommending them. Though the Select Series 10400mAh wasn’t as fast as our top pick and had only around 65 percent of the available capacity, it typically sells for about half the price of our top pick. If you can find it and can live with its shortcomings, it’s worth considering.
offered a unique dual input so that you could charge it with either a Micro-USB or Lightning-connector cable. It offered a handy design that let Apple users carry just a single cable to charge both the pack and their devices. But it still had only two output ports, a dealbreaker for high-capacity batteries such as this.
For Quick Charge 3.0
offers nearly identical features at a similar price to our current Quick Charge 3.0 pick. Although the Thunder can charge two devices at a time, we found in our tests that it could charge only one of the devices at full speed, topping out at a combined 3 A. Our pick, the Tronsmart Presto, can charge two devices at full speed simultaneously, making it much more versatile. Plus, the thinner profile of the Presto is more likely to fit in tight pockets than the Thunder, which is a bit fatter and larger than a deck of playing cards.
both performed well, utilizing full QC 3.0 speeds when charging other devices as well as when we refilled them from a compatible wall charger. But both packs are slightly more expensive and slightly larger than the Tronsmart Presto 10000 PBT10. Further, neither offers the second charging port that makes the Presto convenient as an everyday pack and when you need to power more than one device.
We previously considered the
for its USB-C port, but it technically qualifies as a QC 3.0 battery pack, too. We dismissed this pack, as we did our previous Quick Charge pick, the , and the newer version, the , for this update as being too large and expensive to carry every day.
is another large QC 3.0 pack that isn’t well-suited for everyday duty. Aside from the size, this confusing model tries to do a little of everything by offering both QC 3.0 charging (exclusive to Android devices) and a Lightning input (exclusive to Apple devices). If you are one of the few people who can utilize both features regularly, you’ve found your pack. But the combination isn’t worth the high price for most shoppers.
Previous competition
Though we’ve removed some of our earlier recommendations and dismissals because they’re no longer available, a few older packs are still for sale. The
tested well but lacks the extra built-in cable of the TravelCard and generally sells for a little more. The
offer great build quality and higher (2 A) charging than most other small chargers provide. However, the LithiumCard’s capacity wasn’t as exceptional as its output—we found in testing that it had only about 4 Wh (0.84 Ah) of available power. The
was a previous runner-up pick, but it wasn’t consistently available for purchase and it doesn’t offer the convenience or value of our most-recent picks. We were unable to get any combination of the
ports to put out more than about 2.1 A simultaneously. The few Astro-series batteries that Anker still has available, like the , can’t put out quite as much power simultaneously as newer packs. Even though they’re often available for a discount, we wouldn’t recommend them as good options for the long term.
We’re interested in testing Tylt’s
as a contender for our
category. Although we’ve refrained from picking Tylt power banks in the past due to their high cost, the Slim Boost sells for about $25 (roughly the same as our , the ).
Special thanks to all our friends at Cadex, especially Gary Kwok, applications engineering manager, who spent many hours running tests and interpreting data for us during our 2015 update, and David Oliver, director of product sales and marketing, who helped coordinate the entire project.
Isidor Buchmann,
, testing session
Gary Kwok, , interview