A portable charger, sometimes called a power bank, is a reusable battery that's small enough to fit in your hand. Covered by a protective casing, it connects to any input and output source, allowing you to charge various devices (a smartphone or a laptop, for example) from almost anywhere without the need for a wall outlet.

Portable chargers come in a variety of forms and have a range of features. The most essential aspect is that these chargers have a rechargeable battery built-in that extends the power and use time of your other devices.

Smartphones use battery capacities measured in milliamp hours. These capacities range between 2,000mAh and 5,000mAh, though there are occasional differences. Typical battery banks used for powering phones and laptops also have battery capacity measured in milliamp hours, which makes it easy to determine which size charger you need for a specific device.

How Portable Chargers Work

Instead of charging your phone, tablet, or another device from a wall outlet, you charge it from the power stored in the portable charger by inserting the charger (or charger cable) into the device that needs power.

Given the short lifespan of many smartphones, the popular and best portable chargers are USB devices. These usually are on the smaller side and can easily come along with you in a pocket or purse and extend your phone's battery life. 

Portable chargers are often equipped with one or more USB ports and can connect to nearly any variety of cable used to charge modern smartphones. Standard Micro-USB, USB-C, and Apple Lightning cables ending with a USB Type-A are the common connections you'll need to use with a portable charger.

How to Use a Portable Charger

Portable chargers come in an incredible variety. That means there's no hard-and-fast rule about how these chargers work or how to charge them. Many of the smaller portable chargers recharge over Micro-USB or USB Type-C connections. Larger battery banks may use DC connectors like those found on laptops and other electronics. There are also solar-powered portable chargers on the market.

Power banks charge like other electronic devices with a rechargeable battery. Some may charge faster because of the connector or because a smaller-capacity battery recharges more quickly.

To charge a device using a portable charger, connect the device to the portable charger, and turn on the charger's power. It begins charging the dead or low-powered device. Some chargers provide an indicator that shows when the charge is done; some do not.

What Else Can Portable Chargers Do?

While the most basic portable chargers only offer a USB output to charge one device, other (usually more expensive) chargers offer a host of special features. Some offer support for quick charging technologies, letting you top up your smartphone extra quickly. Some include multiple USB ports, so you can keep multiple devices charging at the same time.

Some portable chargers offer more utility, with three-prong outlets, DC power, and flashlights. Some portable chargers for laptops store a ton of power to keep energy-hungry computers powered. There are also specialized power banks for jumping cars that include a port to connect alligator-clip cables.

Some portable chargers offer charging for a single-use only. Single-use portable chargers can be handy in some situations and are good for tight budgets. Multiple-use chargers are a better choice for people who frequently need to recharge devices when away from home.