How to Choose a Power Bank: mAh vs. Real Capacity, Ports, and Safety Features
I. Decoding Core Parameters of Power Banks: Understanding the True Capabilities Behind the Labels
Actual Capacity vs. Labeled mAh
Core Misconception: The mAh (milliampere-hour) marked on a power bank refers to the cell capacity. The actual usable output capacity is affected by voltage conversion efficiency and device power consumption, not the labeled value.
Test Data: Industry standards require that the actual output capacity of a power bank be no less than 60% of the labeled capacity, with high-quality products reaching 75%-85%. A power bank labeled 20000mAh can actually fully charge an iPhone 15 (battery capacity approximately 3300mAh) 4.5 times and a Samsung S24 Ultra (battery capacity approximately 5000mAh) 3 times, rather than the theoretical 6 times.
Calculation Logic: Actual usable capacity = Labeled capacity × Voltage conversion efficiency (converting 3.7V cell voltage to 5V output voltage). Ordinary power banks have a conversion efficiency of 70%-75%, while products supporting PD fast charging can reach 80%-85%.
Output Power: Determines Charging Speed
Key Significance: Output power (e.g., 18W, 30W, 65W) directly affects device charging speed and must match the fast charging power supported by the device.
Test Comparison: When the iPhone 15 uses an 18W PD power bank, it can be charged to 50% in 30 minutes; using a 30W PD power bank (compatible with 18W output), it can be charged to 52% in 30 minutes, with a negligible speed difference. For Android flagship phones (supporting 65W fast charging), using a 65W power bank can charge to 70% in 30 minutes, while using an 18W power bank only reaches 35%.
Protocol Compatibility: Pay attention to the fast charging protocols supported by the power bank (PD, QC, SCP, etc.). For example, Huawei phones require a power bank supporting the SCP protocol to trigger 66W fast charging; otherwise, they will only charge at a normal 18W power.
Port Types: Adapting to Different Device Needs
USB-C Bidirectional Fast Charging Port
Core Advantages: Supports both charging (input) and discharging (output) bidirectional fast charging, compatible with multiple devices such as mobile phones, laptops, and tablets. It is the current mainstream interface, supporting a maximum output power of 100W.
Adaptation Scenarios: Apple iPhone, MacBook, Android flagship phones, thin and light laptops (e.g., Lenovo Xiaoxin Air). A single Type-C cable can achieve bidirectional fast charging, offering stronger portability.
USB-A Port
Core Features: Only supports discharge output, commonly found in entry-level power banks. The power is mostly 5V/2A (10W) or 18W QC fast charging, with wide compatibility but slow speed.
Adaptation Scenarios: Low-power devices such as old feature phones, Bluetooth headsets, and smart watches, or devices without a Type-C interface.
Detailed Comparison:
Dual-port (1A1C) power banks are more practical, allowing simultaneous charging of two devices. Triple-port (2A1C) models are suitable for users with multiple devices but are 15%-20% larger and heavier.
Safety Features: Avoiding Battery Damage and Safety Risks
Core Protection Mechanisms: Regular power banks must be equipped with six major functions: overcharge protection, overvoltage protection, overcurrent protection, short circuit protection, temperature protection, and foreign object detection. Some high-end products also support battery balancing protection.
Test Standards: According to national 3C certification requirements, a power bank must automatically power off when the battery voltage reaches 4.35V during overcharge testing; temperature protection must stop output when the internal temperature exceeds 60℃.
Material Details: High-quality power banks use flame-retardant ABS or aluminum alloy for the shell, lithium-polymer batteries (safer than traditional lithium batteries, less prone to leakage and explosion) for the cells, and PCB hard board design for internal circuits, offering stronger shock and drop resistance.
II. Power Bank Purchase Formulas Based on Usage Scenarios
Daily Commuting Scenario
Core Needs: Portability first, meeting 1-2 mobile phone recharges, with weight controlled within 200g.
Purchase Formula: 10000mAh (actual capacity approximately 7500mAh) + 18W-30W PD fast charging + 1A1C dual ports + lithium-polymer cells.
Test Adaptation: This configuration can fully charge an iPhone 15 twice and a mid-range Android phone (4000mAh battery) 1.8 times, weighing about 180g, which can be easily put into a pocket or small bag.
Daily Life Scenario Example: Commuter Xiao Li spends 2 hours commuting to and from work every day, and his mobile phone consumes about 30% of its power during the commute. He carries a 10000mAh slim power bank, fully charged before going out in the morning. Charging his phone for 1 hour before getting off work can restore it to 80%, eliminating low-battery anxiety. The power bank weighs only as much as an apple and does not add burden to his backpack.
Short-Distance Travel Scenario
Core Needs: Large capacity + multi-device adaptation, meeting 1-2 days of charging needs, supporting simultaneous charging of mobile phones, headsets, and tablets.
Purchase Formula: 20000mAh (actual capacity approximately 15000mAh) + 30W-65W PD fast charging + 2A1C triple ports + Gallium Nitride (optional) + digital power display.
Test Adaptation: It can fully charge an iPhone 15 4.5 times, an iPad Air twice, and AirPods 8 times. Models supporting 65W output can also provide emergency charging for thin and light laptops (e.g., 13-inch MacBook Air, charged to 40% in 30 minutes).
Detailed Suggestions: Choose a model with a digital power display to accurately check the remaining power; a 20000mAh power bank made of Gallium Nitride is 25% smaller than traditional models, making it more suitable for travel.
Outdoor Office Scenario
Core Needs: High power + long battery life, supporting laptop fast charging, with durability and safety.
Test Adaptation: 65W power can fully charge a Lenovo Xiaoxin Air 14 (65W fast charging) 1.2 times and an iPhone 15 4.5 times; 100W power can fully charge a 14-inch MacBook Pro (96W fast charging) 0.8 times, meeting the power supply needs for temporary outdoor office work.
Safety Notes: In outdoor environments, avoid exposing the power bank to direct sunlight or rain. Aluminum alloy shells have 30% better heat dissipation than ABS materials, making them more suitable for long-term high-power output.
III. Key Considerations to Avoid Pitfalls When Purchasing
Reject False Capacity Claims: Tests show that the actual capacity of no-name power banks is often only 40%-50% of the labeled value. For example, a product labeled 20000mAh may only have 8000mAh. Choose branded products with 3C certification and clearly marked “actual output capacity”.
Do Not Blindly Pursue High Power: If only used for mobile phone charging, 18W-30W power is sufficient. 65W-100W high-power power banks are larger, more expensive, and will not increase charging speed when used for mobile phones.
Pay Attention to Cell Cycle Life: High-quality power banks have a cell cycle life of ≥1000 times, and the capacity remains above 80% of the initial value after 1000 cycles. No-name products usually have a cycle life of only 300-500 times, and the capacity will drop significantly after about 1 year of use.
Be Wary of Low-Price Inferior Products: A 10000mAh power bank priced below 50 yuan is likely to use inferior cells and simplified circuits, lacking basic safety protections. It is prone to heating, swelling, and even explosion during charging.
