Power Bank Buying Guide: 6 Essential Specs to Check Before You Buy

A power bank is an accessory almost everyone needs, yet the shelf holds hundreds of models with near-identical numbers. Many people buy on mAh alone, then find the pack is too heavy, too slow or a poor match for their device.

This guide explains the 6 specs to check before buying one and suggests how to choose for your needs.

1. Choose a power bank by how you use it

Use	Suggested capacity	Suggested output
Daily commute	5,000–10,000 mAh	20 W
Trips of a few days, two devices	20,000 mAh	20–30 W
Charging a laptop or tablet	20,000–27,000 mAh	45–65 W or more

2. 6 specs to check when buying a power bank

Spec 1: Capacity (mAh and Wh)

mAh tells you how much charge the pack holds. More capacity means more recharges, but also more weight. Besides mAh, look for the Wh (watt-hour) figure printed on the case. You can work it out: Wh = mAh x 3.7 / 1,000. For example, 20,000 mAh is about 74 Wh.

Spec 2: Real-world capacity

The printed mAh is the capacity of the cells inside. When charging a phone, some energy is lost to voltage conversion and heat, so the usable share is typically about 60–70%. A 10,000 mAh pack therefore fills a 5,000 mAh phone a little more than once, not twice.

Spec 3: Output power (W)

Wattage sets charging speed. For phones, choose 20 W or more. For laptops that charge over USB-C, you need 45–65 W depending on the model. Note that the headline figure is usually the maximum for a single port; with several devices plugged in, the power is shared.

Spec 4: Fast-charging standard

USB Power Delivery (PD) is the most widely supported standard, working with iPhones, many Android phones, tablets and laptops. Some phone brands use their own fast-charging systems; another brand’s pack will still charge them, but perhaps not at top speed.

Spec 5: Ports

Prefer a USB-C port that works for both input and output, so one cable does everything. An extra USB-A port is handy for older accessories. Check the input wattage too: a 20,000 mAh pack that only accepts 10 W takes many hours to refill.

Spec 6: Safety and airline rules

Buy from a clearly identified brand that lists full specifications and protections against overheating, overcurrent and short circuits. When flying, it must go in carry-on baggage, never checked. According to the FAA PackSafe guidance, the standard limit is 100 Wh per battery; 101–160 Wh needs airline approval. Airlines may be stricter, so check before you travel.

⚠️ Note: Stop using the pack at once if it swells, gets unusually hot, smells of burning, or has been dropped hard or soaked.

3. Tips to make a power bank last longer

• Avoid heat: do not leave it in a car, on a dashboard or in direct sun.
• Do not store it empty: if rarely used, top it up to about half every few months.
• Use a good cable: poor cables charge slowly and run hot.
• Avoid charging and discharging at the same time unless the maker says it is supported.

4. Summary: which power bank to choose

For most people, a 10,000 mAh pack with USB-C PD at 20 W or more from a reputable brand covers a full day. If you travel often or need to charge a laptop, step up to 20,000 mAh and 45 W or more, and check the Wh figure if you fly regularly.

More from our Technology section: Free Up Phone Storage: 6 Easy Steps to Clear Space When Your Phone Is Full and Software Updates on Your Phone and Computer: Why You Shouldn’t Skip Them and 6 Steps to Update Safely.

Frequently asked questions about power banks

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What capacity do you carry? Tell us in the comments! 🔋⚡