Power Bank | mAh vs Watt-Hours: Real Capacity Explained

Power Banks

Introduction

When your phone battery dips into the red, a power bank can be a lifesaver. But not all power banks are created equal, and terms like mAh, watt-hours, and real capacity can be confusing.

In this blog, we’ll break down what these terms mean and how to choose a power bank that truly meets your needs.

What Does mAh Mean in Power Banks? 🔋

mAh stands for milliampere-hour — the most commonly advertised rating on power banks. It measures the battery’s capacity, or how much charge it can store.

For example:

• A 10,000 mAh power bank can theoretically charge a 3,000 mAh smartphone battery about 2.5 to 3 times, considering conversion loss.

• However, mAh only tells part of the story, especially when different devices run at different voltages.

Watt-Hours (Wh): A More Accurate Measure ⚡

Unlike mAh, watt-hours (Wh) take voltage into account and provide a better idea of the actual power delivered.

💡 Formula: Wh = (mAh × Voltage) ÷ 1000

So if a 10,000 mAh power bank operates at 3.7V, it provides: (10,000 × 3.7) ÷ 1000 = 37 Wh

This is more useful when comparing power banks or checking airline safety limits (usually up to 100 Wh is allowed in carry-on).

Real Capacity vs. Advertised Capacity 🧮

Here’s the catch — the advertised mAh is based on the internal battery voltage (3.7V), but your device charges at 5V or higher.

Due to:

• Voltage conversion

• Heat dissipation

• Circuit inefficiencies

You lose 15–30% of the energy. So your 10,000 mAh bank may only deliver 6,500–7,000 mAh effectively at 5V.

How Many Times Can It Charge My Phone? 📱

Let’s break it down with an example:

• Your Phone Battery: 4,000 mAh

• Power Bank (real output): ~6,800 mAh (after conversion loss)

👉 Your phone can be charged once fully and a second time up to ~70% before the power bank is empty.

Quick Charging & Output Ratings Matter 🔌

Beyond just mAh, look for output specs like:

• 5V/2A or 5V/3A (standard fast charge)

• USB-C PD (Power Delivery) for laptops and modern phones

• QC (Quick Charge) 3.0/4.0 support

These determine how fast and compatible the power bank is with your devices.

Air Travel with Power Banks ✈️

Most airlines allow power banks below 100 Wh in your carry-on bag. Check the Wh rating before you fly. A typical 10,000–20,000 mAh power bank is usually within safe limits.

Quick Buying Tips 💡

Feature	What to Look For
Capacity (mAh)	10,000–20,000 mAh for daily users
Output	At least 2A, preferably with USB-C PD
Input	USB-C input for fast recharging
Build Quality	Reputable brand + overcharge protection
Weight & Size	Balance between portability and power

Choose the Right Power Bank

Conclusion ✅

Understanding how mAh, Wh, and real-world efficiency play into your power bank’s performance will help you make a smarter buying decision. Don't just go by the biggest number on the box — look under the hood and consider how it fits your charging needs, speed expectations, and travel habits.

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