What is a power bank and how does it work?

💡 Need to know

• Power to go. It's a battery you charge ahead of time, then carry.
• Capacity isn't speed. More mAh means more charges, not faster ones.
• Must be a match. Your device, cable, and bank all have to support the same charging standard.
• High heat warning. A warm power bank is normal; one that’s hot to the touch is not.

We’ve all been there: You have 14% battery left with no outlet nearby, so you have to pause your work at the most unfortunate time. Fortunately, one item can help you avoid situations like these in the future: a power bank.

At Asurion, we help people set up and understand technology so they can get the most out of their devices. Here’s our guide on what power banks are, how they work, and how you can use them to charge your tech on the go.

What is a power bank, and how does it work?

A power bank is a rechargeable battery pack that stores energy so you can charge a device without an outlet. The process of using one generally follows these steps:

1. You charge the power bank at a wall outlet before you need it.
2. The power bank holds that energy in internal lithium-ion or lithium-polymer cells.
3. While you’re away from a wall outlet, your device runs low on battery.
4. You connect your device to the power bank with a compatible charging cord, and the power bank's internal electronics manage the output to charge your device.

What do power bank capacity and wattage mean?

When you shop around for power banks, you’ll notice two statistics in each product description: capacity (in milliampere-hours (mAh) or watt-hours (Wh)) and wattage (in Watts).

• The mAh measures capacity at a stated voltage. It tells you the size of the power bank’s internal fuel tank—how many times you can charge a device before the power bank runs empty.
• The wattage expresses electrical power output. Watts describe how fast power moves. USB Power Delivery is the standard that lets a bank and a device negotiate how much power to send.

Choose a higher wattage power bank to charge your phone faster, and don’t worry if a power bank has a high maximum wattage. It won’t force wattage into a device that can't accept it.

How to use a power bank safely

Use a power bank safely with these steps:

1. Check the manufacturer's instructions for details on which ports to use when charging your device, depending on its power needs.
2. Look over the bank and cable for damage.
3. Connect your device to a supported output on the power bank with a suitable cable, or set it on the wireless pad if the model has one.
4. Confirm charging has started; press the power button only if the model requires it.

After use, charge your power bank back up so it's ready for next time.

Why isn't your power bank charging your device?

If you plug your device into your power bank and nothing happens, you may be facing a couple of different issues. Try these steps to fix them:

• Confirm whether the power bank is charged.
• Check that your cable is plugged into the right output port on the power bank.
• Check the cable for damage and confirm it supports the charging standard involved.

You can also try to charge the device with a known-good wall charger and cable. If the device charges fine from the wall, the problem is the power bank. If your Android phone won't charge or your iPhone won't charge from multiple known-good charging setups, the device is the more likely culprit. Look for signs of a damaged charging port, which may require repair or replacement by a pro—like the ones at your nearby uBreakiFix by Asurion.

FAQ

Is a power bank the same as a portable charger?

Yep. The terms are usually interchangeable. Both describe a rechargeable battery you carry with you to charge your devices away from an outlet.

How many times can a power bank charge your phone?

It depends on the power bank’s capacity and your phone’s battery size. A higher mAh rating generally means more charges before the power bank needs a recharge.

Is it safe to leave your phone charging on a power bank overnight?

It’s better to unplug once your phone is charged. And if the power bank gets unusually hot, swollen, or damaged, stop using it.

Can a power bank damage your phone battery?

A compatible, undamaged power bank shouldn’t hurt your battery. Use the right cable and charging standard, and skip any power bank that looks damaged or gets extremely hot.

How long does a power bank hold its charge when not in use?

Power banks slowly lose charge while sitting around. If yours has been tucked in a drawer for a while, top it off before you head out.

Can you bring a power bank on a plane?

Usually, yes—but power banks typically belong in your carry-on, not checked luggage. Capacity limits can apply, so check your airline’s rules before packing.