Capacity is only the beginning
A capacity rating describes the cells inside the power bank, not the exact energy your phone receives. Conversion losses are normal. Treat the printed number as a comparison point and look for credible information about usable output rather than assuming every milliamp-hour reaches the device.
Match the output
Check the maximum output of the built-in cable and every port. A large capacity does not guarantee fast charging. Your device, cable and power bank must support compatible charging standards for the fastest advertised result.
Inspect the cable design
A short built-in cable reduces clutter, but it is also a permanently attached wear point. Look for strain relief, a useful length and a separate port that still lets you charge if the integrated cable becomes damaged.
Choose for the trip
For a small daily bag, low weight can matter more than maximum capacity. For longer travel, prioritize capacity, clear battery indication and the ability to charge more than one device. Confirm airline rules with your carrier before flying.