You see "mAh" and "Wh" on battery specs, and while you know they relate to capacity, the real difference isn't always clear. This can lead to miscalculating performance and violating shipping rules.
A Watt-hour (Wh) is a unit of energy, not capacity. It represents the true "fuel tank" size of your battery by combining both its capacity (Ah) and voltage (V). It is the most accurate measure of a battery's total energy.
As a procurement manager, you live by the numbers. But relying on the wrong metric can be a costly mistake. Milliam-hour (mAh) only tells you half the story. The Watt-hour (Wh) gives you the complete picture, allowing for true apples-to-apples comparisons. It's the number that dictates flight time, defines power output, and is the sole metric that matters for airline regulations. Let's break down why it's the most important number on your battery's label.
Why is 'mAh' Not Enough to Compare Batteries?
You have two 10,000mAh batteries, but one gives a much longer flight time. It’s a frustrating situation because the main capacity number seems equal. This confusion can lead to poor procurement decisions.
mAh measures electric charge, but it completely ignores the crucial factor of voltage. A higher voltage battery with the same mAh rating will always have more total energy (Watt-hours) and deliver more power.
I see this all the time. A client will compare a power bank to a drone battery based on mAh and wonder about the price difference. The answer is voltage. Think of it like this: mAh is the amount of fuel, but voltage is the power of that fuel. You can have ten liters of regular gasoline or ten liters of high-octane rocket fuel—the volume is the same, but the energy output is vastly different. The Watt-hour calculation combines both factors to give you the total energy.
The formula is simple: Watt-hours (Wh) = Voltage (V) × Amp-hours (Ah). (Remember to convert mAh to Ah by dividing by 1,000)
Let's look at a practical example:
| Battery Spec | Battery A (Drone Pack) | Battery B (Power Bank) |
|---|---|---|
| Capacity | 10,000mAh (10Ah) | 10,000mAh (10Ah) |
| Voltage | 22.2V (6S) | 3.7V (1S) |
| Total Energy (Wh) | 22.2V × 10Ah = 222 Wh | 3.7V × 10Ah = 37 Wh |
As you can see, even though both are "10,000mAh" batteries, the drone pack holds six times more energy. This is why it can power a high-demand aerial platform while the power bank can only charge a phone. For procurement, comparing batteries by Wh is the only way to make an informed decision.
How Do Watt-Hours Affect Flight Time and Regulations?
You need to calculate realistic flight times for your operations and also comply with strict airline shipping rules. A mistake in calculation can ground your fleet or get a critical shipment rejected by regulators.
Flight time is a direct function of a battery's Watt-hours divided by the drone's power draw in Watts. Furthermore, all international air transport regulations for batteries are based exclusively on Watt-hours, making it a non-negotiable metric.
The Watt-hour is where the theoretical specs meet real-world application. For your drone operations, it dictates two of the most important factors: performance and logistics.
1. Estimating Flight Time
At its core, flight time is a simple energy equation. If you know how much energy your drone consumes on average to stay airborne (its power draw in Watts) and you know how much energy your battery holds (its capacity in Watt-hours), you can estimate your flight time.
The basic formula is: Flight Time (in hours) = Battery Energy (Wh) / Average Drone Power (W)
For example, if your mapping drone consumes an average of 450 Watts to hover, and you are using our 222 Wh KKLIPO battery:
222 Wh / 450 W = 0.49 hours, which is approximately 29.6 minutes.
This simple calculation is fundamental for mission planning and selecting the right battery for the job.
2. Complying with Airline Regulations
This is where understanding Watt-hours becomes a matter of legal compliance. Airline authorities like IATA and the FAA don't care about mAh. Their safety rules are built entirely around the total energy of a battery, measured in Wh.
- Under 100 Wh: Generally allowed in carry-on luggage.
- 100 Wh to 160 Wh: Allowed in carry-on, but requires airline approval and is usually limited to two spare batteries per person.
- Over 160 Wh: Strictly forbidden on passenger aircraft. These must be shipped as fully declared Class 9 Dangerous Goods via a certified cargo carrier.
A 20,000mAh power bank (at 3.7V) is 74 Wh and is perfectly fine to carry on. But a 20,000mAh drone battery (at 22.2V) is 444 Wh and is absolutely forbidden. As a procurement manager, using Wh on all shipping manifests and travel documents is mandatory.
What's the Difference Between a Watt and a Watt-Hour?
The terms "Watt" and "Watt-hour" are often used interchangeably in conversation, which can cause serious confusion. This can lead to misinterpreting a drone's power needs versus a battery's energy capacity.
A Watt (W) is a unit of power—the rate at which energy is used, like speed in km/h. A Watt-hour (Wh) is a unit of energy—the total amount of "fuel" available, like the total distance you can travel.
Getting this distinction right is key to understanding any electrical system. A mistake can lead to buying a battery that can't supply enough power or one that doesn't have enough energy. The easiest way to remember it is with an analogy.
Let's use a water hose:
- Watt (Power): This is the flow rate of water coming out of the hose (e.g., liters per minute). It's an instantaneous measurement. A drone motor pulling 100 Watts is like a hose flowing at a specific rate.
- Watt-hour (Energy): This is the total amount of water you have in your tank to supply the hose. It's a measure of total volume. Your battery's Wh rating is the size of your water tank.
You need a tank (Wh) big enough to last your entire job, and you need a hose and pump (the battery's discharge rating) powerful enough to meet the drone's immediate water flow demands (W).
Here's how they relate in the context of your work:
| Metric | What It Measures | Analogy | Application for Drones |
|---|---|---|---|
| Watt (W) | Power (Rate of energy use) | Speed (km/h) | How much power the drone's motors are drawing right now to hover or climb. |
| Watt-hour (Wh) | Energy (Total capacity) | Fuel in the tank (liters) | How much total "fuel" the battery holds; this is the primary factor in determining flight time. |
Conclusion
Watt-hour is the true, universal measure of a battery's energy. It is essential for accurate performance comparison, flight time calculation, and ensuring you comply with all shipping regulations.