1. Definition and purpose
A power bank (portable power bank) is a portable energy storage device with a built-in lithium-ion battery that charges electronic devices such as smartphones, tablets, and headphones through a USB interface. It solves the problem of low device battery when going out, and is a "life-saving tool" for daily commuting, travel, and business trips.
2. Core parameter analysis
Battery capacity
The unit is milliampere hour (mAh), such as 10000mAh and 20000mAh. The larger the value, the more electricity is stored, but the larger the volume and weight. Pay attention to distinguishing between "nominal capacity" and "rated capacity": for example, a 10000mAh power bank can actually charge a phone with approximately 6000-7000mAh (due to energy conversion losses).
interface type
Input interface: Charge the power bank itself, commonly using Micro USB (old model) and Type-C (mainstream).
Output interface: Charging the device, divided into USB-A (traditional large mouth) and Type-C (supporting fast charging). Some power banks also come with a Lightning interface (Apple specific).
Fast charging protocol
A power bank that supports protocols such as PD (Apple/Android universal), QC (Qualcomm), Huawei FCP, etc., can achieve fast charging for compatible devices (such as 50% charging in 30 minutes).
safety protection 
Overcharge protection, short circuit protection, temperature control and other functions are essential to avoid explosions or damage to equipment.
3. Common types
By capacity
Small capacity (5000-10000mAh): Lightweight and portable, suitable for short distance travel.
Large capacity (20000mAh or above): Suitable for long-distance travel, but attention should be paid to civil aviation carrying restrictions (usually ≤ 27000mAh).
By Function
Basic version: Only provides USB output.
Wireless charging model: Supports Qi protocol, charging can be done by simply putting your phone on it.
Comes with a built-in Type-C/Lightning cable to avoid forgetting the data cable.
Solar powered model: equipped with solar panels, suitable for outdoor emergency use (with lower charging efficiency).
4. Precautions for use
safety first
Avoid high temperatures (such as direct sunlight inside the car), moisture, or heavy pressure.
Choose a legitimate brand and reject products with three no's (easy to falsely label capacity or have safety hazards).
Extend life
When not in use for a long time, keep around 50% of the battery stored.
Avoid frequent full charging and discharging, and use at least once a month.
Civil Aviation Regulations
Rated capacity ≤ 100Wh (approximately 27000mAh) can be carried directly without declaration; Approval from the airline is required for exceeding.