We spent 15 hours researching nearly 30 USB battery packs, eliminating models that were either too expensive, too bulky, or too short on storage. We settled on 5 finalists based on their ratios of size, weight, and cost compared to the advertised capacity. We then had an electrical engineer spend almost 245 hours testing these finalists in order to find that the $30 IntoCircuit Power Castle 11,200 mAh is the USB power bank that most travelers should carry in their bags or briefcases. Little touches like an LCD that displays the remaining charge by percentage and automatically starting to charge devices you plug in without a button press make it feel more thoughtfully designed than the competition. It’s also the battery pack that held the most mAh per dollar.
The IntoCircuit Power Castle can keep a smartphone running for a few days away from an outlet, and it can add hours to the life of a big tablet when you’re stuck on a long flight. Portable USB battery packs are a dime a dozen, but this one saves space, weight, time, and money—even if just a little bit of each.
If our top pick is sold out, or you really think you’ll need the extra juice, the $40 RAVPower Deluxe 14,000 mAh is our runner-up. However, you should know that it was noticeably slower to charge other gadgets and itself. This isn’t a huge deal, but it can be annoying if you often find yourself in a bit of a rush. Some users also report hearing a slight, high-pitched whine that may or may not be noticeable to you.
Our electrical engineer spent nearly 245 hours monitoring the charge and discharge cycles of these power banks as they were hooked up to an iPad and an Android phone. We measured some surprising real-world behaviors that aren’t revealed on spec sheets, like charging inefficiencies and underpowered currents; those results flipped some of our early predictions on their heads.
Who Needs This?
A USB battery pack (also known as a power bank) like the Power Castle comes in handy when you’re away from reliable power for a few days at a time. Think of situations like a road trip, or when you’re bouncing between airports, or if you end up in a region without electricity. It’ll charge one smartphone or one small tablet somewhere between two to five times, depending on the capacity of the battery in your particular gadgets.
It’s also useful when you’re burning through battery life very quickly, like during long days at a tradeshow/conference or long flights across whole oceans or continents. It’ll add precious hours to the life of a 10-inch iPad or keep a handful of smaller gadgets up and running.
The Power Castle is not the right power bank if you’re looking for something to carry in your pocket or purse every day.
The Power Castle is not the right power bank if you’re looking for something to carry in your pocket or purse every day in case your phone needs a little juice before you get home. There are smaller, lighter packs for those purposes, though they only hold about half as much energy. (We know that we’ve promised to cover those, but we haven’t made a pick yet—sorry.) This also isn’t the right battery for intensive power needs like charging a laptop. It can’t crank out enough voltage to fully recharge those kinds of high-drain batteries.
How We Picked
This version of the guide is an update to a pick we made in March 2013, so we used our previous criteria as a baseline to look for new contenders. Our targets were in the neighborhood of 10,000 mAh, $50, 8 ounces, and the dimensions of a thick Android phone. We ended up looking closely at about 30 power banks that met the initial criteria.
As a category, USB power banks have seen some steady improvements in the past year. Capacities have risen, prices dropped, and weights and dimensions remained relatively steady. More models advertise 2.1 A and even 2.4 A ports, which allow for faster charging of devices that support those high-draw amperages. This allowed us to raise our standards for minimum specs.
Our USB travel power bank finalists, from left to right: Satechi Portable Energy Station, RAVPower Deluxe, IntoCircuit Power Castle, Anker Astro E5, Limefuel Blast L130X.
Not too many editorial outlets write comparative reviews of USB battery packs. The few that do only post one-off user reports. There’s almost no empirical data about real-world performance or how power banks compare to one another. So though we read all the reviews that we could find, we didn’t use them as a main source for any of our decisions.
The biggest factors in our choice of finalists were the ratios of weight, volume, and cost against the advertised capacity of each pack. We didn’t set any hard and fast rules, but the banks that we chose can hold close to 300 mAh per dollar, more than 1,100 mAh per ounce, and at least 1,000 mAh per cubic inch.
We settled on 5 models to test. Our previous pick, the Satechi Portable Energy Station 10,000 mAh, received a free pass into the finals on pedigree, even though the capacity is low and the price is high by this year’s standards. Other finalists included theLimefuel Blast L130X 13,000 mAh ($40), Anker Astro E5 15,000 mAh ($50),IntoCircuit Power Castle 11,200 mAh ($30), and the RavPower Deluxe 14,000 mAh($40). They all cost $50 or less, weigh less than 12 ounces, and are no thicker than an inch. Two models have one 2 A port, two models have one 2.1 A port, and the last model has dual 2.4 A ports.
Our testing setup included a bench ammeter to measure the current and mAh output from each power bank into gadgets like the 3rd-gen iPad, pictured.
Our house electrical engineer (formerly of NASA’s Jet Propulsion Laboratory) Sam Gordon explained that these power banks basically consist of 3 components. The lithium-ion battery dictates how much power the thing can actually store. The voltage converter determines the sweet spot of efficiency at the expected output current. And the logic board monitors and regulates the flow of energy from a wall charger into the bank and from the bank into the gadget it’s charging. The logic board also determines how the pack interfaces with the gadgets you plug in. A good power bank needs all three of these to work well in order to efficiently charge itself and devices that are plugged into it. With that in mind, Sam devised a handful of tests to measure the packs’ true capacities, discharge currents, and any odd behaviors that might not otherwise appear on a spec sheet.
The first test measured each pack’s actual capacity and how long it took for the pack to charge up completely. We started by completely draining each power bank. Then, one at a time, we hooked each pack up to a wall charger. Using an ammeter and a laptop running tracking software, we measured how many mAh passed into each power bank, how long it took to reach maximum capacity, and the curve of the input current over time.
In the second test, we measured how fast and how efficiently each pack charges a third-generation iPad. The battery in this tablet is absolutely massive, with a capacity of 11,560 mAh, and it’s designed to take a 10 watt charger—roughly 5 V at 2 A. Put another way, it pushes travel packs toward their limits. Instead of a wall charger, we connected an iPad to each power bank through its highest-draw port (either 2 A, 2.1 A, or 2.4 A, depending on the model). To make sure the iPad never hit a full charge, we played a 10-hour YouTube video so that there would be a constant drain on the battery.
The third test measured how quickly and efficiently each bank charged a Nexus 5 smartphone. We used a similar procedure to the iPad charge test but used the 1 A ports on each pack and left the Nexus 5 in Google Maps Navigation mode to ensure that the battery never reached full capacity. The phone has a 2,300 mAh battery and is designed to work with a 5 V, 1.2 A output charger.
The final test measured maximum amperage. In our three previous tests, we believe that the ammeter and extra cables all introduced extra resistance in the circuit, which reduced the current. So this time we ran a quick test, using a cable with an inline ammeter instead of the separate bench ammeter, to gauge the maximum output current from each pack’s highest-draw port.
Our Pick
The IntoCircuit Power Castle offered the most mAh per dollar without being too bulky. Devices start charging automatically, and a built-in LCD tells you how much juice is left. For a typical smartphone, you’re looking at a few days of extra life.
It’s the smallest pack by volume, weighs less than 10 ounces, and holds the most mAh per dollar.
After accounting for size, price, capacity, and all the quirks that turned up during testing, theIntoCircuit Power Castle 11,200 mAh emerged as the best travel buddy if you’ll be on the road for two days or longer. It’s the smallest pack by volume, weighs less than 10 ounces, and holds the most mAh per dollar. The charge and discharge rates are the fastest we measured, which gives it an edge when it comes to last-minute travel prep or situations where you desperately need a little bit of juice in your phone. It’s also the only finalist with a numerical charge indicator, which is as close as any of these packs come to having a user interface.
The IntoCircuit Power Castle 11,200 mAh has two output ports, a numerical charge-level indicator, and even a built-in flashlight.
Based on our test results, here’s an estimate of how many battery cycles a fully juiced Power Castle 11,200 mAh will provide to some popular phones and tablets, accounting for inefficiency of transfer:
| iPhone 5S: |
4.5 cycles |
| iPad (3rd Gen): |
0.6 cycles |
| iPad Air: |
0.75 cycles |
| iPad Mini with Retina: |
1 cycle |
| Samsung Galaxy S5: |
2.5 cycles |
| Nexus 5: |
3 cycles |
| Nexus 7: |
1.5 cycles |
That’s a couple extra days of battery life for the most power-hungry phones. And even with a full-size, energy-guzzling tablet like the third-generation iPad, the Power Castle provides enough of a charge to watch around three extra movies. If you do the math, you’ll note that these figures are significantly lower than the advertised maximum, but that’s not due to false-advertising (usually). Rather, this power loss is due to inefficiencies inherent to transferring energy from one battery to another via USB, something that all power banks have to deal with.
The Power Castle has one 5 V / 2.1 A output for tablets and other high-draw devices, and one 5 V / 1 A output for phones and other low-draw devices. It can simultaneously charge one device in each port. Though there are other packs with 2.1 A outputs (and the Limefuel even has two 2.4 A outputs), the Power Castle juiced up an iPad faster than any other finalists.
It also charged itself at a marginally faster rate than any of the other packs, storing 1,000 mAh for every 1.05 hours it was plugged in.
Looking beyond its performance, the Power Castle’s build quality and design also give it a slight edge over most of its competitors. It feels like it’s built to hold up on the road over months and months of use. Weighing in at a shade under 10 ounces, it’s not exactly feather-light, but it’s still an ounce or two lighter than some other top packs. It also takes up the least space in your bag by a few fractions of a cubic inch, at 2.8 x 4.3 x 0.9 inches.
The faux brushed-metal plastic cover adds a bit of texture to help prevent the pack from sliding off a table (and looks classier than other plasticky packs, if that matters to you). Compared to the $130 Mophie Powerstation XL—the power bank you’ve probably seen at Best Buy, the Apple Store, or some shop at the airport—the IntoCircuit feels just as sturdy but is smaller by volume and weighs about 33 percent less, all while somehow ringing up $100 cheaper.
The Power Castle can charge two gadgets at the same time.
Our favorite interface touch is the LCD with the bank’s remaining charge level by percentage. (Other packs just use four or five LED indicators.) The number changes steadily as it charges or discharges, whereas the indicators on other packs only change in intervals of 20 or 25 percent of the bank’s capacity. It’s reassuring to be able to monitor the levels as closely as you can with the Power Castle.
The Power Castle also automatically begins charging devices when they’re first connected. Other packs require you to press a button to start the process.
Flaws but not dealbreakers
The Power Castle’s advertised capacity is lower than some of its competitors, and it’s somewhat less efficient than many of them. Compared to the 14,000 mAh RavPower Deluxe (and after factoring in inefficiencies—the IntoCircuit is somewhat less efficient than its competitors), it’s missing more than a cycle’s worth of energy for a phone. A few people will need that extra capacity. But for most travelers, the Power Castle will get through most situations with no problem, so we think it makes sense to save the weight, space, and money.
The Power Castle doesn’t come with its own AC adapter (though you probably have enough of those already), and owners are quick to point out that there’s no Lightning Cable attachment. We suppose those are fair gripes, though most banks don’t come with their own charger, and none come with a Lightning Cable. Use the one that came with your phone, or buy a spare. On the plus side, it does come with a USB to micro USB cable, plus a second USB cable that accepts five included dongles for mini USB, 30-pin, and a few feature phone plugs.
When the pack says it’s at 50 percent, it’s probably closer to 25 or 30 percent…
The most common gripe we heard about the Power Castle is that below a certain threshold, the charge indicator is just not very accurate. When the pack says it’s at 50 percent, it’s probably closer to 25 or 30 percent and the count will start to drop pretty fast, based on user feedback and our own experience. That’s not ideal, but some of the packs with the 4-LED indicator system demonstrate the same behavior, if user reviews are to be believed.
Pass-through charging—that is, charging the power bank while it, in turn, charges other gadgets—isn’t supported. Most other packs don’t have this feature either.
It doesn’t have the same volume of user reviews as other power banks, which means that we’re less likely to hear about potential problems. At the time of writing, there are 161 Amazon user reviews for an excellent average of 4.6 stars. Only 12 of those reviews are 3 stars or less. Some commenters mentioned that IntoCircuit offers a $10 gift certificate to verified buyers who leave a 5-star review, which is sketchy. But even if that user score is artificially inflated, the Power Castle proved itself in our testing, and is still cheap, light, and small. Some user reviewers were shipped duds, and as with any piece of low-cost electronics, there’s a chance that’ll happen to you, so buy from somewhere with a good return policy—and try to do it more than two days before your vacation starts. (Let us know if you run into that problem.)
The runner-up
If you can’t find the IntoCircuit, we suggest the RAVPower as a solid second choice. It’s a tad more expensive with a bit more mAh to offer, but it was markedly slower to charge (both itself and gadgets): keep that in mind.
If the IntoCircuit Power Castle is sold out, or you’ll travel more comfortably knowing you have an extra day of battery power for your phone, our runner-up choice is the RavPower Deluxe 14,000 mAh. It has a huge capacity, netting about an extra day of smartphone battery life or a few extra hours for a big tablet. At just a shade over 10 ounces, it has average heft for the category, and it carries the most energy by weight. It also holds the most energy by volume. At at $40, the price is still very reasonable.
A few things stopped us from making it our main pick. Charging and discharging are pretty slow compared to the Power Castle. It took 17 hours to fully charge this thing, about 1.22 hours per 1,000 mAh. Its fastest port is 2 A, not 2.1 A or 2.4 A, and our test results showed that it charged an iPad at a slower rate than most other power banks.
The RavPower Deluxe is also fairly large, about a half-inch longer and wider than the IntoCircuit, with only marginally less depth, so it won’t be as easy to pack. It also has the lowest Amazon user rating among our finalists, though an average of 4.3 stars over 477 ratings is pretty great in most categories. A few users complained about a high-pitched “squeeee” noise while it’s charging, though we couldn’t hear it—if you’re older than 35 or have been to a few Slayer shows, that part of your hearing is probably gone now.
What to look forward to
We can obviously expect to see packs with higher capacities, and they’ll get marginally smaller and lighter. We’ll also see more packs with 2.4 A outputs. Not too many gadgets can draw that amperage yet, but since there’s no harm in charging a phone through a high-output port, expect to see more manufacturers future-proofing their packs by incorporating 2.4 A slots.
We know we’ve promised a pick for a smaller, lighter power pack for daily carry in a pocket or handbag. We don’t have one yet. Sorry!
The Competition
The Satechi Energy Station 10,000 mAh, our pick in last year’s guide, still has plenty of redeeming qualities. It weighs just 7.5 ounces, or about 25% less than the IntoCircuit Power Castle. Wirecutter founder Brian Lam likes its long, rectangular shape because he finds it easier to pack than more square-shaped packs, though your mileage may vary. At this point, however, it’s the most expensive power bank in the group (at $60) with the lowest capacity (at 10,000 mAh). It charges slow, too. It was a great pick a year ago, but times have changed, even if the Satechi’s price hasn’t.
…it’s the most expensive power bank in the group (at $60) with the lowest capacity (at 10,000 mAh).
Early in our research, the Anker Astro E5 looked like a frontrunner. It has the highest capacity in the group, 15,000 mAh, and it seemed to have solid ratios of capacity against weight, volume, and cost. The Amazon user reviews are excellent, and the spec sheet listed a fast 2.1 A output. But we got some weird results in our tests, even after testing two different units. The current swings wildly while it charges, as much as 0.7 A each second. What might be even stranger is that the efficiency and discharge times are nearly on par with other packs. You might ask: if the results are OK, what’s the harm? Our electrical engineer believes that the behavior could damage the components in the pack and lead to a much shorter lifespan for the product.
We let Anker know about our results after the initial test. They believed the pack to be defective, so they sent us a replacement. We measured very similar results from that pack, too. We tried getting in touch with an Anker engineer or product manager, but had not heard anything from them at the time of writing. We honestly don’t know if what we measured will have an effect on real-world performance. But there are a few other solid packs to pick from, and they all show normal charging behavior, so we’re setting this one aside.
We scoped out the Limefuel Blast L130X 13,000 mAh because it has two 2.4 A ports for charging two high-draw devices at once. It’s coated in a grippy rubber material so that it won’t slip. For $40, that’s great. But the test results were middle-of-the-road at best. Our electrical engineer said that it acted like a prototype that was released a bit too early. This is a new company and they’re off to a solid start, but this is not the pack to buy right now.
We looked at quite a few other packs as well, most of which received easy dismissals on price, capacity, weight, or size.
The Mophie Powerstation is the power bank you’re most likely to find at brick-and-mortar stores like Best Buy, the Apple Store, or the last-minute electronics shops at any airport. We briefly looked at the 12,000 mAh version, the Powerstation XL, but it weighs almost a full pound and costs $130. Those are non-starters.
The New Trent PowerPak+ NT135T almost made our group of finalists. It was a little too big, a little too expensive, and its best output port is a little underpowered. Not quite there yet. We’d also already dismissed New Trent’s iCarrier and iGeek batteries after testing them in our 2013 roundup.
The Anker Astro 3 2nd Gen has dual 1.5 A ports and a third 2.4 A port, but there aren’t many gadgets that benefit from those hookups (not yet, anyway). And at $50 for 12,000 mAh, the capacity per dollar is lower than we were able to find elsewhere.
The uNu Enerpak Vault is massive—1 inch thick, 7.5 inches long, and 4.5 inches across. That’s one of the lowest capacities per cubic inch that you’ll find, and it’s not easy to pack. The capacity per dollar is mediocre as well.
The Patriot FUEL+ costs $71 for 9,000 mAh, which is a terrible mAh to price ratio, and none of the new models they announced at CES 2014 looked like better deals, either.
The Incipio offGrid costs $47 for 8,000 mAh, which is a mediocre ratio and a significantly lower capacity than you can find elsewhere.
The Lepow Moonstone only holds 6,000 mAh, which is not much juice if you’re away from an outlet for more than a day or so.
We also briefly looked at other packs from Cobra, Eton, ZAGG, Braven, Jumpr, and Hyper (no, this was not the lineup for Lollapalooza 1994), and we dismissed them all on price, capacity, and size.
Wrapping it up
If you’re hitting the road, bring the IntoCircuit Power Castle 11,200 mAh with you. It’ll help keep your gadgets powered up even if you’re away from an outlet for a few days, and it’s the best balance of cost, capacity, and size that we could find.
This guide originally appeared on The Wirecutter on 6/6/2014 and is republished here with permission.
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Works on Gnats too!
