How Power Banks Work: The Science Behind Charging (and Why Some Explode)

How Power Banks Work: The Science Behind Charging (and Why Some Explode)

Introduction

A power bank seems simple: charge it, then charge your phone. But beneath the surface lies a complex dance of lithium ions, circuit boards, and safety mechanisms. This guide explains why some power banks die after 6 months—and others last 3 years.

1. The Two Types of Batteries Inside

18650 Lithium-Ion Cells:

Pros: Cheap, high discharge rate.

Cons: Prone to swelling (cycle life ≈ 300 charges), used in budget models.

Li-Polymer Cells:

Pros: Flexible, longer life (cycle life ≈ 500 charges), safer.

Cons: 30% more expensive, so often skipped in low-end models.

2. The “Brain” of the Power Bank: Smart IC Chips

These tiny chips manage:

Voltage Regulation: Prevents overcharging (your phone won’t exceed 4.2V).

Temperature Control: Shuts down if internal temps hit 60°C (common in fast-charging models).

Protocol Matching: Talks to your device to deliver the right power (e.g., 5W for earbuds, 27W for iPhone 16).

3. Why Cheap Power Banks Explode

No Overcurrent Protection: A short circuit can’t be stopped.

Fake Capacity Labels: A 5,000mAh cell labeled as 10,000mAh leads to overheating.

Poorly Welded Connections: Vibration (e.g., in a backpack) causes internal shorts.

Conclusion

When shopping, look for brands that disclose battery type (Li-polymer is safer) and certifications (UL 2056 is the gold standard for power banks).