When shopping for a portable charger, numbers like 10,000mAh or 99Wh often dominate product descriptions. At first glance, they look similar—but they don’t mean the same thing. For anyone choosing a power bank, understanding these measurements is the key to making the right decision.
This article breaks down the difference between milliampere-hours (mAh) and watt-hours (Wh), why both matter, and how to read these numbers to match your real charging needs.
What Does mAh Mean?
mAh (milliampere-hours) is a unit that measures electric charge. It tells you how much current a battery can provide over time.
- A rating of 10,000mAh means the battery can theoretically deliver 10,000 milliamps for one hour, or 1,000 milliamps for 10 hours.
- In practice, the actual usable capacity is lower due to efficiency losses and voltage differences.
mAh is the most common figure used in marketing power banks, because it’s a simple number that consumers recognize. However, it doesn’t tell the whole story.
What Does Wh Mean?
Wh (watt-hours) measures total energy capacity. It combines both current and voltage into one figure.
- Formula: Wh = (mAh × Voltage) ÷ 1000
- Example: A 10,000mAh battery at 3.7V = (10,000 × 3.7) ÷ 1000 = 37Wh
Unlike mAh, which only shows charge, Wh represents the actual amount of energy stored—making it a more universal measurement.
Wh is especially important when considering:
- Airline regulations (most allow batteries under 100Wh in carry-on luggage).
- Comparing different devices (since not all batteries operate at the same voltage).
Why Both Units Appear on Power Banks
Manufacturers often highlight mAh because it makes the product look impressive—big numbers sell. But Wh is the standard engineers and regulators use to measure true energy.
For example:
- A 27,000mAh pack sounds huge, but if its nominal voltage is 3.7V, that’s about 100Wh.
- A 10,000mAh pack at 5V output provides closer to 50Wh, depending on conversion efficiency.
So, two power banks with different mAh ratings might actually have similar Wh values once you factor in voltage.
How to Compare Capacities Accurately
Convert mAh to Wh
Always calculate watt-hours for a fair comparison. Use the formula with the listed voltage (often 3.6V or 3.7V for lithium-ion cells).
Check Output Voltage
Charging a phone at 5V vs a laptop at 20V will drain the same Wh at different rates. Higher voltage outputs consume stored energy faster.
Consider Efficiency Losses
Converting stored energy into usable USB output isn’t perfect. Heat and circuitry reduce efficiency, so expect 10–20% loss.
Match Device Needs
Smartphones typically need 10–15Wh per full charge.
Tablets range from 25–40Wh.
Laptops vary widely, from 40Wh for ultrabooks to 80–100Wh for high-performance models.
Everyday Examples
Example 1: Charging a Smartphone
- Phone battery: ~3,500mAh at 3.8V ≈ 13Wh.
- A 10,000mAh power bank (≈37Wh) could theoretically recharge it almost 3 times.
- After efficiency losses, real-world performance is closer to 2.5 charges.
Example 2: Charging a Laptop
- Laptop battery: 60Wh.
- A 20,000mAh bank (≈74Wh) could recharge it once, but may not fully replenish depending on voltage demands and efficiency.
Example 3: Airline Rules
- Airlines limit carry-on batteries to 100Wh.
- This is roughly equal to 27,000mAh at 3.7V.
- That’s why many “travel-friendly” high-capacity banks are designed just under this threshold.
Common Misunderstandings
- “Higher mAh always means better.”
Not true. A 20,000mAh pack at a lower voltage may deliver less usable energy than a 15,000mAh pack at a higher voltage. - “My 10,000mAh charger will always recharge my 3,000mAh phone three times.”
Not exactly—conversion losses, voltage differences, and phone usage during charging reduce efficiency. - “mAh is the international standard.”
Airlines, engineers, and safety regulators rely on Wh for a universal measurement.
Practical Tips for Buyers
- Look for Wh, not just mAh. If a product doesn’t list it, calculate it.
- Check your device battery specs. Compare their Wh rating with the bank’s.
- Mind the 100Wh airline rule. Especially important for frequent travellers.
- Balance portability and capacity. A 5,000mAh bank may be enough for daily use; 20,000mAh+ suits trips and laptops.
- Don’t ignore output wattage. Even with enough Wh, the bank must support high-watt outputs to charge laptops or drones.
Future of Power Bank Ratings
The industry is gradually shifting toward transparency. More brands now list both mAh and Wh, along with supported charging protocols like USB-C PD. Expect clearer labelling as consumers become more aware of how these numbers affect real-world performance.
Conclusion
Understanding the difference between mAh and Wh transforms the way you shop for portable chargers. mAh gives a sense of charge capacity, while Wh reveals the true energy inside. By converting between the two, accounting for voltage, and matching capacity to your devices, you’ll choose a power bank that meets your real needs—whether that’s a pocket-sized backup for your phone or a high-capacity unit that keeps your laptop alive on long journeys.
Armed with this knowledge, you can finally see past the marketing numbers and buy with confidence.
