The Best Power Bank

Buying Guide

Tablets. Smartphones. Smartwatches. Laptops. We’ve got so much gear these days that sometimes we can forget that these devices need power — until that power gauge goes into the red. When that happens, you understand how essential a good power bank can be, especially if you’re on vacation or miles away from a convenient wall plug in the wild.

In situations like those, a good power bank can literally be a lifesaver. But exactly what are they? First, let’s talk about what they are not. While power banks can charge your phone or other devices, they are not technically chargers. Chargers are just conduits between your phone and a power source (typically a wall outlet). Power banks are the power source, packing an internal battery that your gadgets can hook up to and feed on.

Those internal batteries can be one of two types: Lithium-ion (usually listed as Li-Ion) or the less common lithium polymer (Li-Po).

Lithium-ion batteries were first developed in the early 1910s and they are still in common usage today — with several improvements to those first crude models. These batteries can pack a lot of power into a relatively small package, and they’re relatively cheap to produce. They’re not without their drawbacks, however. Lithium-ion batteries will degrade more easily over time, and can even be unstable — although that’s more likely to be the fault of the device and not the battery inside it. (For a prime example, look up the 2016 woes of Samsung’s Galaxy Note 7).

Lithium polymer batteries, by comparison, are less likely to leak electrolytes and therefore a bit safer. They’re also lighter, more flexible and can be made much thinner. So why aren’t they the standard? Like most technology that’s smaller and sleeker, they are significantly more costly to make. Nor are they necessarily better, depending on your energy needs. In general, they can’t pack the same amount of power into as small of a space as lithium-ion, and their ability to recharge can degrade slightly over time.

Mind you, looking at the type of battery you have won’t tell you how much energy your power bank can supply. For that, you’ll have to look at the battery capacity, which is measured in mAh. That stands for milliamp hours, and it takes a bit of explaining. Milliamps are a unit of measurement for electric current equal to one-thousandth of an ampere. Milliamp hours will tell you the energy capacity of a battery by telling you how long your power bank can supply a certain amount of energy. In terms of charging up your phone, let’s say it has a battery capacity of 2,000 mAh. If you have a power bank with a battery capacity of 10,000 mAh, it could charge up your phone five times without needing a recharge itself. Simple division: 2,000 times 5.

Enjoy the practice, because you may want to do a little more easy math before shopping. Take a look at all your devices and add up their own battery capacity. That’s the number you’ll probably want as a minimum for your own power bank, provided you plan on charging multiple gadgets with it. The battery capacity for smartphones can vary wildly (especially among older models), but the current iPhone 11 has a capacity of over 3,000 mAh. The latest tablets have batteries that can hold from 5,000 to 9,000 mAh or more. Laptops understandably take a lot more power, so you’ll need a high-end power bank with at least 20,000 mAh if you want more than one full charge at a go.

That’s well and good, but capacity isn’t everything. When you’re on the go, sometimes you don’t have all night to charge up your gear. When you need to know how fast your power bank will deliver a charge, look at the output stats. They’ll be measured in two numbers: Volts (V) and amps (A). Without getting into the electrical weeds too much, these two numbers are multiplied together to get the full output possible, in watts (W). You’ll see proprietary fast-charging tech like Qualcomm’s Quick Charge advertised for certain devices, but those numbers are the bottom line. And bear in mind they may not be the rate at which your device actually charges: Speed is limited by the cable that you use to connect your phone or tablet to the power bank. If the power bank can deliver a charge at 5V / 3A but the cable is only capable of handling 5V / 1A, you’ll charge at the slower rate.

Of course, your power bank itself will eventually have to be recharged. Look for the input stats to get a sense of how fast it can get to a full charge when connected to a standard wall outlet.

So much for the interior stats. One feature that will be immediately obvious in your power bank is how many output ports it has. The more ports, the more devices you can charge simultaneously. Multiple ports might be a major attraction for multi-taskers who like to take all their gear on the go, but all ports are not created equal. USB-A ports will be standard, but there have been several upgrades to that standard over the years. Look for ones with USB 3.0 compatibility or higher, as they’ll be able to take advantage of higher-speed cables.

Some power banks might be capable of wireless charging, and may even be able to do that while providing power to other devices through the USB ports. Just know that the power it puts out will be split between those devices and may not charge any of them as fast as it would solo.

Of course, all this functionality doesn’t mean much if your power bank weighs as much as a generator. Yes, modern power banks keep a relatively slim profile. Some may be as small as your smartphone itself, or even smaller. Heads up, though: they may be heavier than they look — even ones that have slimmer lithium polymer batteries. Take a look at the weight before purchasing and figure that into your travel plans.

Speaking of travel benefits, many power banks can make themselves useful for more than just a passive charge. Some can use their batteries to power a flashlight in case of emergencies or will heat up just enough to become a makeshift pocket warmer in frigid weather. Those perks can make a lot of difference, and turn a forgotten backup device into a handy hiking buddy.

• So you’ve got your power bank. All set to take your gear on the road? Not so fast. Make sure you’ve got the charging cables to go with it. Strange as it may seem, many power banks won’t provide the connectors that actually attach their battery to the device it needs to charge. Check that you’ve got a cable to match the port type supplied on your power bank (ideally one that matches or exceeds the output speed).
• Make sure you also charge up the power bank before you use it for the first time. Many banks will come with only a minimal charge right out of the box, in order to preserve the battery.
• A good power bank can last for many years if it’s properly stored. Different models may boast of their durability, but no matter what the casing, lithium batteries and moisture do not mix. Keep it out of the rain for extended periods, or submersion in water. A more common pitfall is heat or cold. Your power bank will perform best at room temperature, and it definitely will suffer if left out in a hot car for days on end (or a poorly insulated one in winter, for that matter).