Best Power Banks 2026: Anker, Baseus, and Mophie Tested for Real Capacity and Speed

Power banks are sold with rated capacity that does not equal actual delivered capacity. A 20,000mAh power bank at 3.7V internal cell voltage delivers approximately 13,000-15,000mAh at 5V USB — this is physics, not deception. Conversion losses are always present. This guide explains what specs to evaluate and which power banks actually deliver their stated performance.

Actual vs Rated Capacity

All lithium-ion cells operate at approximately 3.7V internally. USB output is 5V (or higher for USB-PD). The conversion from 3.7V to 5V introduces a 20-25% efficiency loss.

Calculation: 20,000mAh x 3.7V / 5V x 0.85 efficiency = approximately 12,580mAh delivered at 5V USB.

This is why a "20,000mAh" power bank charges your 5,000mAh phone only 2-2.5 times, not 4 times.

The higher the output voltage, the more efficient the conversion:

• USB-PD at 20V (charging a laptop): approximately 20,000mAh x 3.7V / 20V x 0.9 efficiency = 3,700mAh at 20V — about 74Wh, which is what specs typically quote for laptop power banks

When evaluating power banks for laptop charging: look for Wh (watt-hour) rating rather than mAh. Wh is voltage-agnostic and tells you the true energy capacity.

Output Wattage: Matching Bank to Device

Most important spec when buying for laptop charging:

• iPhone 15 Pro Max (USB-PD): needs 27W for fastest charging
• iPad Pro (USB-PD): needs 30W for fastest charging
• MacBook Air M2 (USB-PD): charges at up to 70W
• 14-inch MacBook Pro (USB-PD): charges at up to 96W
• 16-inch MacBook Pro (USB-PD): charges at up to 140W
• Windows gaming laptop (USB-PD): typically 100-140W

A power bank rated at 65W charges a MacBook Air at full speed but charges a 14-inch MacBook Pro slower than the wall adapter. It cannot charge a 16-inch MacBook Pro while it is in use — the laptop will discharge even with the power bank connected.

Rule: match power bank output wattage to at least 90% of your laptop's maximum charging wattage for the bank to maintain or add charge during use.

Input Wattage: Recharge Time

Power bank input wattage determines how long it takes to recharge the bank itself.

• 20W input on a 20,000mAh bank: approximately 8-10 hours
• 45W input: approximately 4-5 hours
• 65W input (Anker 737): approximately 2.5 hours
• 100W input: approximately 2 hours

If you recharge your power bank every night: slow input is acceptable. If you sometimes need to recharge the bank during a workday: high input wattage (65W+) matters.

Airline Carry-On Rules

The US Department of Transportation and most international equivalents allow lithium-ion batteries up to 100Wh in carry-on luggage without approval; 100-160Wh with airline approval (carrier-specific policy); over 160Wh is generally not permitted.

Converting mAh to Wh: mAh x 3.7V / 1000 = Wh

• 20,000mAh: approximately 74Wh (permitted without approval)
• 26,800mAh: approximately 99Wh (permitted without approval, close to limit)
• 27,000mAh: approximately 100Wh (at the limit — some airlines require approval)
• 30,000mAh: approximately 111Wh (requires airline approval on most carriers)
• 40,000mAh: approximately 148Wh (requires approval, some carriers prohibit)

For international travel: stay under 100Wh (approximately 26,800mAh) to avoid any restrictions. The Anker 737 (24,000mAh / 88.8Wh) fits under 100Wh.

Number of Ports: Planning for Multiple Devices

When traveling with laptop, phone, earbuds, and smartwatch: a single-port power bank forces sequential charging. Two-port banks allow simultaneous charging but split the total output wattage.

Example: Anker 737 at 140W max output with two USB-C ports simultaneously: typically 70-100W to the primary device, 20-30W to the secondary. This is adequate for simultaneously charging a laptop (70W) and phone (25W).

Check that the power bank specifies simultaneous multi-port output, not just individual port ratings. Some banks rate each port independently but limit total output when multiple ports are used.