Power Bank Buying Guide 2026: Capacity, Wattage, and Airline Rules Explained

The power bank category has more misleading marketing per square inch of packaging than almost any other consumer electronics category. This guide explains what the numbers mean and how to buy correctly.

The Capacity Deception: mAh vs Wh

Power banks are marketed in mAh (milliamp hours). This unit is only meaningful at a specific voltage — and power banks output at multiple voltages (5V, 9V, 12V, 15V, 20V depending on device negotiation).

The correct unit for comparing power bank capacity is Wh (watt hours). Every power bank that ships for sale in the EU must display Wh. In the US, many manufacturers display only mAh.

Convert mAh to Wh: Wh = mAh × V / 1000

For internal lithium cells: V = 3.7V

10,000mAh power bank: 10,000 × 3.7 / 1000 = 37Wh
20,000mAh: 74Wh
26,800mAh: 99.2Wh (just under the 100Wh airline limit)
30,000mAh: 111Wh (over 100Wh limit)

Charging efficiency (conversion from internal 3.7V to output 5V USB-A): approximately 80-85%.

So a 20,000mAh / 74Wh power bank delivers approximately 59-63Wh to devices — enough for approximately 2 iPhone 15 charges (from an 11.1Wh battery) or 0.6 of a MacBook Air charge.

Matching Wattage to Your Device

For smartphone charging only (27W max for most modern phones):

Any 18W+ USB-C PD power bank is adequate
The bank's capacity (mAh/Wh) determines how many charges you get
Output wattage above 30W is not useful for phone-only use

For iPad Pro charging (45W max):

45W+ USB-C PD required for fast charging
20W or 30W banks charge iPad Pro slowly but still charge it

For MacBook Air or thin laptop (65-70W max):

65W+ USB-C PD output required to charge at full speed while plugged in
Below 65W: laptop charges more slowly than normal but still gains charge while idle

For 14-inch MacBook Pro (96W max):

96W+ output: full speed charging
65-95W: slower than wall adapter but adds charge while laptop is used lightly
Below 65W: laptop may still lose charge under active workloads

For 16-inch MacBook Pro (140W max):

140W output: only Anker 737 in mainstream category
100W: laptop charges while in light use; may lose charge under heavy processing
65W: laptop maintains charge only when idle

Fast Charging Standards: What They Mean

Multiple fast charging standards exist and they are not all compatible:

USB Power Delivery (USB-PD): the universal standard. Works with all USB-C devices that support fast charging (iPhones, iPads, MacBooks, most modern Android phones, Windows laptops). All power banks in this guide support USB-PD.

Qualcomm Quick Charge: proprietary standard for Qualcomm Snapdragon-based Android phones. Many power banks support QC 3.0 or QC 4.0. QC-compatible banks charge Samsung Galaxy S-series, Pixel phones faster than standard USB-PD.

Huawei SuperCharge / VOOC / OPPO: proprietary standards for specific brands. Not relevant for most users.

For most users: USB-PD support is sufficient. If you have a Qualcomm-based Android phone: USB-PD + QC compatibility provides the fastest charging from a power bank.

The Airline 100Wh Limit: Exact Rules

US DOT (Department of Transportation) lithium battery regulations, which apply to commercial flights:

Under 100Wh: allowed in carry-on without airline approval
100-160Wh: allowed in carry-on with airline approval (contact carrier before travel)
Over 160Wh: generally prohibited on commercial flights

The 100Wh threshold: approximately 27,000mAh at 3.7V.

Practical rule for no-hassle air travel: stay at or under 100Wh (approximately 26,800mAh). The Anker 737 at 88.8Wh fits this limit.

Note: 100Wh is per battery. You can carry multiple batteries under 100Wh. Two 74Wh power banks is 148Wh total — both are under 100Wh individually and permitted.

Checked luggage: lithium batteries must be in carry-on. Checked luggage with loose lithium batteries is not permitted on most carriers.

Passthrough Charging: When It Matters

Passthrough allows a power bank to charge from the wall while simultaneously outputting to a device. Useful scenarios:

One outlet, two devices (charge power bank and phone simultaneously from one adapter)
Power bank runs low during a meeting — charge it and keep it connected to your laptop

Passthrough efficiency varies: some banks throttle output significantly when charging themselves. The Anker 737 maintains good output wattage during pass-through. Check reviews for watt-meter measurements if this feature is important.

Number of Ports and Simultaneous Charging

For single-device charging: one port is sufficient. For travel with multiple devices: two USB-C ports allows simultaneous laptop + phone charging.

Important: total output wattage is typically shared across ports. A 140W power bank with two USB-C ports may deliver 100W + 30W simultaneously, not 140W + 140W. Check the spec sheet for simultaneous multi-port wattage.

Recharge Time for the Power Bank Itself

Often overlooked: how long does it take to recharge the power bank?

10W input on 20,000mAh bank: 12-14 hours (overnight minimum)
25W input: 5-6 hours
45W input: 3-4 hours
65W input (Anker 737): 2.5 hours

For daily commuters who recharge overnight: input wattage is irrelevant. For travelers who might need to recharge mid-trip: look for 45W+ input.

Size and Weight for Daily Carry

Three size categories for everyday use:

Pocket power banks (under 200g, under 10,000mAh): fits in jeans or jacket pocket. Charges phones 1-2 times. Does not charge laptops effectively. Good for: day trips without a bag.

Bag power banks (200-500g, 10,000-20,000mAh): fits in any laptop bag or backpack. Charges phones 3-5 times, most laptops once at 65-100W output. Good for: daily office commute.

Heavy-duty travel banks (500-700g, 20,000-27,000mAh, 100-140W): heavier than most external hard drives. Best for: travel days where multiple full device charges are needed.

Do not buy a 641g power bank thinking you will carry it daily. Match size and weight to how you actually carry your bags.