To USB charge a power bank, follow these steps: Connect a compatible USB cable to the power bank's input port. Attach the cable to a USB-powered device such as a computer, wall adapter, or car charger. Ensure the power bank supports USB input (most modern models do). The device will then draw power from the power bank, replenishing its battery. Avoid using non-certified cables or adapters to prevent compatibility issues or damage.

USB charging relies on standardized power delivery defined by USB specifications. USB 2.0 and USB 3.0 outline voltage (5V) and current (up to 0.5A for USB 2.0, 0.9A for USB 3.0) requirements, enabling power banks to transfer energy efficiently. According to the USB-Implementers Forum (USB-IF), over 90% of power banks sold globally since 2020 include USB-A or USB-C input ports, reflecting industry adoption of universal compatibility. However, output capabilities vary: a 10,000mAh power bank with 18W output can replenish a phone's battery up to 50% in 30 minutes when paired with a USB-C PD adapter, as noted in a 2022 USB-IF report.

Key limitations include voltage mismatch and power bank capacity. For example, a 3A/5V USB port can deliver 15W, but a power bank with a 10W input threshold will only accept up to that limit. A 2023 study by Statista found that 35% of users encounter charging failures due to incompatible cables or insufficient input power. Additionally, USB-IF certification ensures adherence to safety and efficiency standards, reducing risks like overheating. Always verify a power bank's input specifications (e.g., USB-A/USB-C, voltage, current) against the connected device's requirements to optimize charging speed and longevity.