Difference Between mAh and Wh: Things to Know Before Buying
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When shopping for a power bank, you’ll almost always run into two big numbers: mAh and Wh. They’re printed on the packaging, plastered across product pages, and often treated like the ultimate measure of battery power. But here’s where confusion kicks in—these two numbers don’t measure the same thing. Understanding the difference between mAh and Wh is critical if you want to avoid buying a power bank that looks powerful on paper but underdelivers in practice.
This isn’t just about decoding technical jargon. It’s about knowing which number actually reflects real battery life, how to compare across brands fairly, and what to watch for when dealing with airline restrictions, charging efficiency, and your device’s unique power needs. Think of it as clearing up the messy world of mAh vs Wh battery specifications, so you can make smarter choices before spending your money.
That’s exactly what this guide is here to do: explain the difference between mAh and Wh, and show you what you really need to know before buying your next power bank.
Let’s get started!
Difference Between mAh and Wh and Why You Should Care
Here’s the thing: battery marketing can be confusing. One brand might flex a massive 30,000 mAh, while another brags about 100 Wh. Without context, those numbers feel impossible to compare—like trying to decide if you’d rather have 10 gallons of gas or 40 liters. Same idea, different units. Understanding the mah vs watt hour is key to making an informed choice.
And when you’re standing in the electronics aisle (or scrolling through online deals), this confusion can mean:
- You end up buying a power bank that looks powerful on paper but dies sooner than you expect.
- You struggle to figure out if a certain model can charge your laptop, not just your phone.
- You might even run into airline restrictions, since airlines measure Wh, not mAh.
So yeah—knowing the mah and wh difference is worth it.
What is mAh?
mAh stands for milliampere-hour. It’s a measure of electric charge. In simple terms, it tells you how many milliamps (a measure of current) a battery can provide for one hour.
- A 10,000 mAh battery can theoretically deliver 10,000 milliamps for one hour.
- Or 1,000 milliamps for 10 hours.
- Or 100 milliamps for 100 hours.
Think of it as how much "juice" the battery holds, without directly telling you the voltage (which matters a lot, as we’ll see in a second).
Why manufacturers love mAh: It makes numbers look big. 20,000 mAh sounds a lot more impressive than 74 Wh, even though they could describe the same exact battery.
What is Wh?
Wh stands for watt-hour. This unit measures energy. It combines both current (amps) and voltage (volts). One watt-hour is the amount of energy used to power a one-watt device for one hour.
So, if you have a 50 Wh battery, it can:
- Power a 50-watt device for 1 hour.
- Or a 10-watt device for 5 hours.
- Or a 5-watt device for 10 hours.
Unlike mAh, Wh directly tells you the actual energy content of the battery, making it more accurate for comparing different devices.
mAh vs Wh Battery Specifications and the Importance of Voltage
Here’s where things click: mAh and Wh are connected, but voltage is the missing link between them.
The relationship is simple:
Wh = (mAh × Voltage) ÷ 1000
This formula translates the charge capacity (mAh) into the actual energy (Wh). For example:
-
A 10,000 mAh battery at 3.7 volts = (10,000 × 3.7) ÷ 1000 = 37 Wh.
Now notice something: that same 10,000 mAh looks much smaller once it’s expressed in watt-hours. This is why manufacturers lean on mAh—it makes the battery seem more impressive. But Wh is the true measure of usable energy. If you’ve ever wondered about the difference between mAh and Wh, this is exactly where the numbers reveal it.
So why does voltage matter? Because not all batteries, or devices, work at the same voltage. Most lithium-ion cells inside power banks have a nominal voltage of around 3.6–3.7V. But when you’re charging a phone over USB, the output needs to be 5V, and for laptops it might need 12V, 15V, or even 20V.
Every time a power bank steps up the voltage to match your device, it burns a little energy in the process. The higher the output voltage, the faster the internal battery drains. That’s why two power banks with the same mAh rating can behave very differently once you plug them into real devices.
In short:
- mAh tells you the raw storage capacity.
- Voltage decides how that capacity is delivered.
- Wh combines both into the real-world energy you can actually use.
When comparing models, checking the Wh rating gives you the clearest picture of what a power bank can actually deliver.
The Real Deal
If you want the short answer: Wh is the more reliable unit.
- mAh is fine for comparing batteries with the same voltage (like most phone power banks).
- Wh gives you the actual energy capacity, which makes it the better choice for apples-to-apples comparisons.
Airlines agree—they only care about Wh when setting limits for carrying power banks on flights. (Most allow up to 100 Wh in carry-on, sometimes up to 160 Wh with approval.)
mAh vs Watt-hour: A Side-by-Side Look
|
Feature |
mAh (milliampere-hour) |
Wh (Watt-hour) |
|
What it Measures |
Electric Charge (size of the tank) |
Energy (the actual fuel in the tank) |
|
Voltage Dependent? |
Yes. The value is meaningless without knowing the voltage. |
No. It is a universal unit of energy, independent of voltage. |
|
Efficiency |
Doesn’t account for conversion losses. Hides inefficiency. |
Accounts for the total available energy. The true capacity. |
|
Usefulness |
A good internal metric, but a poor consumer-facing metric for comparison. |
The best metric for comparing different power banks and understanding real-world performance. |
|
Travel Rules |
Not used by airlines. You'd have to calculate it. |
Directly used. The legal limit for carry-on is usually 100 Wh. |
Tips for Buying the Right Power Bank
So now you know the science. But how do you actually pick a good one? Choosing the right power bank comes down to understanding how manufacturers present mAh vs Wh battery specifications, and knowing how to interpret them. Here are some quick rules:
Tip #1: Seek Out the Wh Rating
Before you even look at the mAh, scan the product listing or the physical box for the Wh rating. If a company is proud enough to list it prominently, it’s generally a good sign. It shows they are transparent about the true power bank battery capacity. If the packaging only lists mAh, you can calculate Wh using the voltage (usually 3.6–3.7V for lithium-ion cells). This practice is essential for truly understanding mah vs watt hour and the real capacity of the battery.
Tip #2: If You Only See mAh, Do the Math (or Use a Rule of Thumb)
Most power banks still only list mAh. That’s okay, you’re a savvy shopper now. Assume the internal voltage is 3.7V.
- Quick Calculation: (Advertised mAh × 3.7) / 1000 = Approximate Wh
- Even Quicker Rule of Thumb: For a rough estimate, take the advertised mAh and multiply by 0.0037. Or, to get the effective 5V mAh, multiply by 0.7-0.8 (accounting for efficiency). A 10,000mAh bank will give you roughly 7,000-8,000mAh of actual phone charge.
Tip #3: Calculate Your Needs in Wh
How many full charges do you actually need? Find your phone’s battery energy in Wh. For example:
- iPhone 15 Pro Max: ~17.11 Wh
- Samsung Galaxy S23 Ultra: ~19.3 Wh
A 50Wh power bank can theoretically charge that iPhone about 50 / 17.11 ≈ 2.92 times. Factoring in 85% efficiency, you’d get a solid 2.5 full charges. This is a far more accurate prediction than using mAh.
Tip #4: Prioritize Brands That List Wh
Companies like XYZtech often list the Wh capacity alongside the mAh. This transparency is a hallmark of a brand that respects its customers and is confident in its product’s real performance.
Tip #5: Beware of "No-Name" Giants
Be extremely wary of ultra-cheap, off-brand power banks advertising astronomical capacities like 50,000mAh or 100,000mAh for $30. The physics and cost of quality lithium cells make these claims almost certainly false. They often have real capacities a fraction of what is advertised. If they don’t list a Wh rating, it’s a major red flag.
Final Thoughts
When comparing power banks, Wh gives you the clearest picture of how much real work the battery can actually do. mAh is like the flashy Instagram filter—it looks good at first glance, but it doesn’t tell the whole story. Here’s the quick breakdown:
- mAh = charge capacity (bigger numbers, but less useful without context).
- Voltage = how that charge is delivered.
- Wh = the real energy you can use.
Understanding the difference between mAh and Wh isn’t about throwing one out—it’s about seeing through the marketing hype. mAh still matters, but only when you also factor in voltage and efficiency. Wh, on the other hand, is the more honest, universally comparable metric.
So next time you’re weighing up mAh vs Wh battery specifications, don’t just chase the biggest mAh number on the box. Check the Wh rating, match it to your devices, and consider efficiency. That way, your power bank won’t just sound powerful—it will actually keep your gadgets alive when you need them most.
Frequently Asked Questions
Q: Does the mAh rating of my power bank matter if I'm using a fast-charging cable?
Yes, it does. While a fast-charging cable and wall adapter can speed up the charging process, they can't change the total energy a power bank holds. A fast charger simply increases the power output (W), which means more energy is delivered in a shorter amount of time. The mAh (or more accurately, the Wh) still represents the total amount of energy available to be delivered. Think of it as a wider hose—it fills the bucket faster, but the bucket's size remains the same.
Q: Do bigger Wh power banks last longer over the years?
Not necessarily. Capacity loss (battery aging) happens to all lithium-ion batteries, typically about 15–20% over two years, regardless of size. A larger Wh unit gives you more buffer, but quality (cell grade, heat management, brand reputation) matters more than size alone when it comes to longevity.
Q: Why do some power banks list both a 3.7V and a 5V rating?
The 3.7V rating refers to the nominal voltage of the internal lithium-ion battery cells. This is the voltage at which the Wh capacity is calculated. The 5V rating, on the other hand, refers to the boosted output voltage that the power bank delivers to charge most standard USB devices. The difference between these voltages is why the total usable capacity is always less than what the initial mAh rating might suggest due to energy conversion loss.
