Understanding Power Bank Physics: A Complete Guide
How to Calculate Power Bank Capacity Manually
Understanding the math behind portable energy is crucial for keeping your devices running. The core formula relies on converting everything into Watt-hours (Wh), which is a universal measure of energy. The formula is: Energy (Wh) = Voltage (V) × Amperage (A) × Time (h). Once you have the total energy required, you must account for the conversion efficiency—usually around 80% for standard lithium-ion batteries—due to heat loss during voltage regulation.
Why Voltage Conversion Matters (3.7V vs 5V)
Marketing labels can be misleading. Most power banks list their capacity in milliampere-hours (mAh) based on the internal battery cell voltage of 3.7 Volts. However, USB devices typically require 5 Volts (or more for laptops). This voltage boost requires energy, meaning a "10,000 mAh" power bank cannot actually deliver 10,000 mAh to your phone. Our SafePower Advisor algorithm automatically performs this conversion to give you the real-world capacity you need to buy.
Critical Safety: Environment & Family
Safety extends beyond the device itself. Keep power banks out of reach of children. Lithium batteries contain toxic chemicals and can cause severe burns or fires if punctured, chewed, or damaged by rough play. Additionally, loose cables present a strangulation risk for infants. regarding the environment, never expose your power bank to water or high humidity (like bathrooms or saunas). Moisture can corrode the internal protection circuits (BMS), leading to dangerous short circuits.
Lithium-Ion Risks (Thermal Runaway)
While generally safe, Li-Ion and Li-Po batteries carry risks if mishandled. Thermal Runaway is a chemical chain reaction occurring when a battery overheats, potentially leading to fire. Always ensure your power bank has built-in protection against overcharging and short-circuiting. Never use a battery that shows signs of swelling, leakage, or physical damage.
How to Choose the Right Power Bank
When selecting a portable charger, verify the Input/Output ports (USB-C PD is recommended), check for certifications like CE, FCC, and RoHS, and ensure the brand uses high-quality battery cells. For air travel, remember that the International Air Transport Association (IATA) typically limits carry-on batteries to a maximum of 100 Watt-hours without special airline approval.