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It always seems like my local coffee shop runs out of outlets right when my smartphone battery is inching toward zero percent or my laptop is on its final legs, and I need to make a call or hail a ride home. Of course, while the coronavirus COVID-19 rages on, most coffee shops are shutting their doors and upwards of 80 million Americans have been ordered to stay indoors. Regardless, the dwindling number of available slots in your surge protectors and power strips or trying to work remotely from different parts of your home could mean a portable charger is in demand. Whether you’re looking for a new one now or trying to replace yesteryear’s model, it can be challenging to find the right portable battery pack for you, considering the sea of technical jargon you’ll be wading through shopping for a new charger. Here’s how to figure out what you need so you can charge your wireless earbuds, laptop, smartphone or travel tech no matter where you are.

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Portable charger capacity: How much can you charge?

How long does a portable charger last? Shopping for a battery pack is a delicate balance between size and capacity. You want something that fits comfortably in your backpack or purse, but you also want it to hold a lot of juice so you can charge up your devices as much as possible.

Charging capacity is often measured in either milliamp-hours (mAh) or watt-hours (Wh). Simply put:

Watt-hours (Wh) will give you the best estimate of how much or how many times the charger can juice up your device.

will give you the best estimate of how much or how many times the charger can juice up your device. Milliamp-hours (mAh) will give you a decent spec to use when comparing different battery packs.

“Watt-hours is a better, more accurate rating of capacity, but phone manufacturers leaned in the direction of milliamp-hours,” explains Brad Saunders, chairman of the USB Promoter Group at the nonprofit USB-IF, which develops and maintains specifications for USB standards. If your battery pack uses watt-hours, just compare the watt-hours on the battery pack to the number of watt-hours held by the device you want to charge. For example, a 12Wh battery could charge a 4Wh device three times — maybe a bit less, due to losses in efficiency.

Milliamp-hours are more problematic. All else equal, they can be useful comparing the capacities of different battery packs: A 5,000mAh battery pack will provide fewer charges than a 12,000mAh model. But milliamp-hours don’t tell enough of the story. Due to certain marketing tricks, you can’t always say that a 12,000mAh battery will charge your 3,000mAh phone exactly three times, for example — it’s more like two, or two-and-a-half. (You can see an example of this in Belkin’s portable charging guide.) At the very least, though, it’ll give you somewhat of a ballpark when you’re shopping among several portable chargers.

Anker’s lipstick-sized PowerCore+ Mini can fit just about anywhere, which makes it perfect for tossing in your pocket or purse. It holds 3,350mAh, which Anker says is enough to fully charge an iPhone 8, or most of a Samsung Galaxy S8. Again, there’s some wiggle room there, but it’s a perfect charger for a day on the town when you might not be able to stretch your battery until bedtime.

The PowerCore 10000 PD Redux is a bigger brother to Anker’s PowerCore+ Mini. It isn’t as pocket-friendly, but consequently it equips a larger charging capacity. 10,000mAh is enough to charge an iPhone XS or Galaxy S10 around two times, and can charge two devices at the same time. (It can also charge modern phones very fast, which we discuss in more detail below.)

Keep in mind that the bigger the device, the bigger battery it likely has. Plus-sized phones like the iPhone 11 Pro Max will need more juice to get to 100 percent than their smaller siblings, while tablets like the 10.2-inch iPad will require even more. Ultimately, you’ll need to balance your charging needs with how much space you have to lug the battery bank around. Personally, I always travel with two: a small battery pack for my pocket (like the PowerCore+ Mini above) and a larger one for my backpack that can get me through multiple charges over multiple days.

Charging speed: How quickly can you charge?

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Just about any battery pack will charge your phone adequately, but some can do it much faster than others. This is particularly useful if your battery’s nearing 0 percent and you need to cram as much juice as possible before you head out the door— but the different fast-charging standards can be a bit confusing.

Charging speeds may be denoted in one of a few ways:

Amps : If one USB port says 1A and the other says 2A, the latter 2 amp port is going to charge your phone faster. It won’t be blazing, but it’ll be a decent step up.

: If one USB port says 1A and the other says 2A, the latter 2 amp port is going to charge your phone faster. It won’t be blazing, but it’ll be a decent step up. Quick Charge (QC) : A few years ago, many phones came with proprietary fast-charging tech. Many used Qualcomm Quick Charge or some variant thereof (sometimes with their own branding on top, like Samsung’s Adaptive Fast Charging and Motorola’s TurboPower). Sometimes you’ll see Quick Charge-branded USB ports on battery packs: If your phone is compatible, it’ll charge even faster through that port.

: A few years ago, many phones came with proprietary fast-charging tech. Many used Qualcomm Quick Charge or some variant thereof (sometimes with their own branding on top, like Samsung’s Adaptive Fast Charging and Motorola’s TurboPower). Sometimes you’ll see Quick Charge-branded USB ports on battery packs: If your phone is compatible, it’ll charge even faster through that port. USB Power Delivery (USB-PD): Many modern phones use a much simpler standard called USB Power Delivery. Your phone can handle chargers up to a certain wattage, and will charge as fast as it can with whatever PD-compatible charger or battery bank you give it. If your phone brands itself as Quick Charge 4.0, it’s compatible with PD as well.

You can see which fast-charging standards your phone supports by checking its page on the manufacturer’s website — the Samsung Galaxy S10, for example, is compatible with QC2.0 and USB-PD.

When in doubt, I recommend buying a newer PD-compatible battery bank if you’re looking for fast charging. It’s the easiest to understand, since it measures charging speed in watts, and will be the most widely supported going forward. Even if you have a pre-PD version of Quick Charge on your phone — like on the Samsung Galaxy S8 or earlier — buying a battery pack with older standards will hamper you the next time you upgrade your phone.

RAVPower’s 20,100mAh power bank can charge modern phones incredibly fast. Its regular USB port can charge at up to 12 watts, while the smaller USB-C port can charge up to 30 watts. That means it can charge an iPhone 11 — which can charge at 18W maximum — up to 50 percent in under 30 minutes.

Just make sure you’re using the right port for the fastest charging possible — you may need to buy a USB-C cable to go with your battery bank if your phone didn’t come with one. When in doubt, says Saunders, look at your phone—it’ll tell you on the lock screen whether it’s “charging rapidly” or not.

Battery pack compatibility: What can you charge?

While pretty much any battery pack will charge your phone or tablet — they don’t need too much power — laptops might have higher requirements. If you’re looking to charge a laptop on-the-go, you’ll either need:

A portable charger with a standard AC outlet like the RAVPower 27000mAh AC power bank

A PD-capable battery pack that provides enough wattage over its USB-C port (provided your laptop can charge over USB-C, of course).

Choosing the right battery pack is just a matter of comparing its wattage to your laptop’s charger. “If it says ‘works best with a charger that’s rated at 27W and higher, then go look for the 27W-and-higher charger, and you’ll get the best experience,” says Saunders. It’ll still work with a 15W charger — in most cases, at least — it’ll just charge slower.

So pull out your laptop’s charger and make note of the number on the bottom. Apple’s latest MacBook Air, for example, comes with a 30W charger. Google’s Pixelbook shows up with a 45W charger. You’ll want to make sure you get a battery pack that matches or exceeds that wattage. You’ll probably a high capacity battery pack, too, since laptops have much larger batteries than phones (and you’ll often find them measured in the more accurate watt-hours, or Wh, in addition to or in lieu of milliamp-hours).

ZMI’s reasonably-priced battery pack should work with most USB-C laptops. It measures its capacity at 20,000mAh or 72Wh, with 45 watts of charging power — enough to charge the aforementioned MacBook Air a little under two times. It’s also ideal for laptops because it doubles as a USB hub, so you can plug flash drives into it while you’re charging your laptop — keeping you from having to give up your precious USB ports just because you’re low on battery.

If you want to charge your laptop faster (especially if you have a higher-end laptop like the 13-inch MacBook Pro), you’ll want an even more powerful battery bank — and Goal Zero’s Sherpa series is a fantastic choice. Not only does it have a tough aluminum build, but it also supports 60W from its USB-C port, has a 94.7Wh capacity—just about the highest that you can legally bring on a plane. It even sports a wireless charging pad, so you can juice up your phone without cables and, if you want, concurrently use its USB ports to charge multiple devices.

Portable charger shopping safety tips

Triple check compatibility. We’re in an interesting period of transition between charging standards, so it’s always a good idea to double-check that a battery bank is going to work well with your phone or laptop before you buy. Read the product description, and Google around or check Amazon reviews to see if someone can confirm a given battery pack works with the model phone or laptop you’re hoping to charge (especially if you want to use fast charging).

Invest in cables. You’ll also want to make sure you have high quality cables—this ensures the fastest charging speed possible, as well as better safety. Saunders naturally recommends cables that have been certified by the USB-IF, who maintains these standards — it’ll often say in the product listing, though you can also search the USB-IF’s database here. Reputable brands like Anker are often a good way to go.

Check for third party certifications. You’ll also want to make sure the battery bank has been certified by organizations like Underwriters Laboratories (UL). Look for that UL label on the box or the product page. (You can also check that same USB-IF database for the battery pack, though there aren’t many battery banks that have gone through their certification process yet — it’s mostly chargers and cables.)

Utilize return policies. Finally, remember to use that return policy. Amazon gives you 30 days to send something back if you don’t like it, for example, so don’t be afraid to use it if a product doesn’t charge your device the way you’d hoped.

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