Whether you call them battery packs, power banks, or portable chargers, these accessories are good at one thing: charging devices when you can’t find an open plug. Battery packs are small enough to fit in a day pack and strong enough to live at the bottom of your carry-on. Depending on the size of the battery, they can charge your phone, tablet, laptop, or even all three at once.

How big of a charger you need and what extra features you might find useful will depend a lot on what you want to charge. Since there are so many choices on the market right now, we tried a bunch of different models to find the best portable power banks you can buy right now.

type of battery
A lithium-ion battery is in almost every rechargeable power bank you can buy, as well as in most portable gadgets. In terms of charge capacity per size, these batteries are better than any others on the market. In fact, their energy density has grown by eight times in the past 14 years. They also don’t have a memory effect, which is when a battery’s life gets shorter when it’s only partly charged.

You may have heard that one problem with lithium ion batteries is that they can catch fire. To make battery packs less dangerous, they have to have built-in controls for things like power and pressure. Even though you should still make sure a battery isn’t stressed out more than it needs to be, like by being overheated, dropped, or used in cold weather, battery packs are safe enough to bring on an airplane. The TSA says that you can fly with external batteries that are 100Wh or less, which is what all of our tips are. Just make sure to pack them in your carry-on, because you can’t put them in your checked luggage.

How much
Manufacturers of power banks almost always show the capacity of a battery in milliamp hours, or mAh. Smaller batteries, like those that can charge a smartphone to between 50 and 75%, usually have a capacity of 5,000mAh. Batteries that are bigger than 25,000mAh can be used to charge computers, tablets, and phones more than once. As expected, the price of most batteries goes up as their capacity goes up. Since batteries are physical storage units, their size and weight also go up as their capacity goes up. If you want more power, you’ll have to pay more money and carry a bigger brick.

You might think that a 10,000mAh power bank could charge a 5,000mAh phone to 100% twice, but that’s not true. Aside from easy energy loss through heat, things like changing the voltage also reduce the amount of power that gets into your phone. Most makers list how many times a smartphone battery can be charged. In our tests, a battery pack with a capacity of 10,000mAh charged a device by about 5,800mAh. Chargers with 20,000mAh gave about 11,250mAh to a device, and chargers with 25,000mAh gave about 16,200mAh. That means that, on average, about 60% of the time was used effectively.

Ports
Even though (thankfully) the tech world is moving toward USB-C as the norm, power banks are still a mixed bag. All of our top choices have at least one USB-C port, and some also have one or two USB-A ports. Newer Android phones charge through USB-C, but iPhones still use the Lightning port. Most newer tablets and computers, including the latest iPads, charge through USB-C.

When a battery pack has more than one port for charging, the ports usually do different things. Most power banks have at least one port that says “in/out,” which means you can use it to charge the bank and your device at the same time. Smartphones and other small devices can be charged with USB-A ports, but bigger devices can’t be charged with them. Plus, they’re not as fast overall as USB-C ports. Think about this when choosing which ports and cords to use to connect your phone to the pack.

Even among USB-C ports, there are more differences. Different ports on the same gadget can transfer power at different speeds. In real life, this means that an iPhone will charge just fine when hooked into the 18W port on a power bank. But for a MacBook or similar laptop to charge fully, it needs the extra power that a 100W port can provide. This is something that larger power banks can do. Power banks with more than one port can also charge multiple devices at once, but at a slower rate and with less power overall.

You should also think about your cable. Use USB-C ports and cables to charge anything bigger than a smartphone or to get fast-charging features. But not every USB-C connection is the same, even if it has the same plug on the end. If you want power from a 100W USB-C port on a power bank, you’ll need a USB-C cord that can handle 100W. Power banks that can give out 100W usually come with a cord that works with the device. We’ve tried and liked Anker’s 100W USB-C cable for devices that don’t have one. We used this 60W cable from Nimble for smaller devices, and we wouldn’t try with anything less than 60W. Higher-capacity cables cost about $20 and will make sure you’re not wasting time with connections that don’t let you send as much power as you could.

Set up
Most battery packs have a squared-off, brick-like shape, but many of them have nice finishing and details that make them look nice. Even though that doesn’t change how they work, it’s something to think about for things you’ll use often. Some portable power stations have extra features, like the ability to work with MagSafe, a built-in wall plug, or a chair. Almost all power banks have some kind of gauge that shows how much charge is left. Usually, this is done with lighted pips near the power button. Some of the biggest banks go one step further and have an LED screen that shows how much power is left. This can be helpful if you’re using a pack for a mobile office or something similar.

Best MagSafe-compatible battery: Spigen ArcHybrid Mag

I went into this category expecting Apple’s own MagSafe battery pack to be a top pick. And while it performed admirably, charging a dead 14 Plus to about 43 percent in an hour and 45 minutes, Spigen’s ArcHybrid delivered a 56 percent charge in nearly the same amount of time. The ArcHybrid firmly attaches to the MagSafe ring and it’s flush enough that you can easily hold your phone and use it while charging up. Unlike the Apple battery, it includes four indicator lights to help you gauge how much juice the pack itself has left. Considering Spigen’s battery is $30 cheaper than Apple’s, it’s easy to recommend.

Alternatively, Anker’s 633 Magnetic battery delivered a larger charge thanks to its 10,000mAh capacity, boosting the iPhone to 100 percent in three hours with enough left over for an additional 29 percent charge. And while the kickstand feature felt mildly useful, the battery itself was bulky – but that’s understandable for a power bank that’s twice as large as Spigen’s. Ultimately, the ArcHybrid performed better as a quick and convenient way to give a partial charge to your iPhone on the go.

It’s important to note that wireless charging is less efficient than wired. Our tests showed wired battery banks deliver a device charge at around 60 percent efficiency. With the wireless chargers, that rate dropped to an average of 46 percent. Something to keep in mind when weighing the costs, both ecological and monetary, of wasted energy.

Specs: 5000mAh, 7.5W max
Ports: One USB-C in/out
Cable: USB-C to USB-C
Number of charges iPhone: 0.56
Charge time iPhone: 0 to 56% in 1h 43m