Power Bank
Overview
A power bank (portable charger, auxiliary battery; 보조배터리) is a portable energy storage device with a built-in lithium-ion or lithium-polymer battery that allows portable electronic devices to be charged while on the move. As usage time for mobile devices such as smartphones has increased and battery-integrated designs have become commonplace, it has established itself as an essential accessory. With the spread of the USB PD (USB Power Delivery) standard, the product lineup is rapidly evolving to support fast charging, laptop-class output, wireless charging, and more.
Main Content
Definition and Operating Principle
A power bank contains rechargeable secondary battery cells and the circuitry that controls them. It receives power from an external source (an adapter), stores it in the battery cells, and when needed converts it via a DC-DC converter to the voltage required by the device (5V, 9V, 12V, 15V, 20V, etc.) for output. In this process, step-up/step-down conversion losses and heat are generated, and energy efficiency is generally in the 60–85% range.
Key Components
- Battery cells: 18650/21700 cylindrical cells or pouch-type lithium-polymer cells
- BMS (Battery Management System): protection against overcharge, overdischarge, overcurrent, short circuits, and overheating
- DC-DC converter: boost and buck circuits
- Charging protocol IC: negotiation chips for USB PD, QC, AFC, SCP, etc.
- Connectors: USB-A, USB-C, micro USB, Lightning, wireless coil
Capacity and Unit Notation
Capacity is expressed in mAh (milliampere-hours) or Wh (watt-hours). Since mAh requires the voltage to be known in order to determine actual energy, international standards (such as for air transport) use Wh. Wh = rated voltage (V) × capacity (Ah); for example, a 3.7V·10,000mAh cell is 37Wh. Rated capacity and the actually usable output capacity differ, and when converted to 5V output it is typically listed at roughly 60–70% of that figure.
Types
- Standard: 5,000–10,000mAh, charges a smartphone 1–2 times
- High-capacity: 20,000–30,000mAh, charges laptops and tablets
- Slim/built-in: case-integrated, direct-plug types (with built-in plug)
- Wireless charging: Qi/Qi2 magnetic alignment types
- Solar/emergency: for camping, disaster preparedness, and combined jump starters
- Docking: ultra-compact products that attach directly to the bottom of a smartphone
Charging Standards and Technology
USB PD is standardized up to a maximum of 240W (PD 3.1 EPR), making it possible to charge laptops and monitors as well. PPS (Programmable Power Supply) finely adjusts voltage and current to reduce heat generation. Qi2 improved wireless charging efficiency and alignment issues through magnetic alignment. Recently, bidirectional charging (combined input/output), simultaneous multi-port output, display-based remaining-capacity indication, and low-current mode (for earbuds and watches) have become standard features.
Safety and Regulation
Lithium batteries carry the risk of thermal runaway and are subject to strict regulation internationally. For air transport, batteries of 100Wh or less may be carried on board, 100–160Wh require airline approval, and those exceeding 160Wh are prohibited. In principle, they cannot be placed in checked baggage. Certification in each country (KC in Korea, UL 2056 in the United States, CE in the EU, CCC in China) must be verified, and low-priced uncertified products carry a high fire risk due to inadequate protection circuits. If swelling, overheating, or damage is observed, use must be stopped immediately.
Market and Applications
The power bank market has grown alongside the spread of smartphones, and recently high-density, high-output products have been increasing as a spin-off of electric vehicle battery technology. Demand for camping, car camping, and disaster preparedness, demand for remote laptop work, and growth in travelers are driving the market. Chinese companies lead the market based on cost competitiveness, while domestic and international brands differentiate themselves through design, safety certification, and charging speed.
Latest Trends
In 2024–2025, products with 140–240W output based on USB PD 3.1 emerged as mainstream, broadening the charging scope to include laptops and small appliances. As the Qi2 wireless charging standard spread to the Android ecosystem, magnetically attachable power banks became popular, and many MagSafe-compatible products were released. Products that apply silicon carbide (SiC) and gallium nitride (GaN) components to reduce volume and increase efficiency have been increasing.
In addition, in Korea, fires involving electric kick scooters and electric bicycles have raised social interest in lithium battery safety management, and the trend is toward strengthening safety certification and labeling obligations for lithium battery products such as power banks. Airlines have reorganized their in-flight power bank regulations, tightening requirements such as banning in-flight charging, attaching insulating tape to terminals, and storing them in overhead bins. Smart displays that show remaining battery capacity as a percentage, app-linked status diagnostics, and used-battery collection and recycling campaigns are also establishing themselves as new trends.
Related Topics
- [[Lithium-ion battery]]
- [[USB PD]]
- [[Wireless charging]]
- [[Smartphone]]
- [[Electric vehicle battery]]