mAh measures current capacity over time, while Wh measures total energy storage – multiply mAh by voltage and divide by 1000 to convert between them.
Understanding battery capacity helps you choose the right portable power station and estimate how long it will power your devices during camping trips or emergencies.
You’ve probably seen both mAh and Wh ratings on batteries and wondered what they actually mean. These numbers tell different stories about your battery’s performance, and knowing the difference can save you from buying the wrong power station for your needs.
What Does mAh Actually Mean?
mAh stands for milliampere-hours. Think of it as measuring how much electric current flows out of your battery over one hour. It’s like measuring water flowing from a garden hose – mAh tells you the flow rate, not the total amount of water in the tank.
A 5000mAh battery can theoretically deliver 5000 milliamperes for one hour, or 1000 milliamperes for five hours. But here’s the catch: mAh doesn’t tell you anything about voltage, which affects the actual power available.
Why mAh Can Be Misleading
Comparing batteries using only mAh is like comparing cars by their gas tank size without considering fuel efficiency. Two batteries with the same mAh rating can have completely different energy capacities if they operate at different voltages.
I found that many people get confused when they buy a 20000mAh power bank expecting it to charge their phone 10 times, but it only manages 6-7 charges. The voltage difference between the power bank’s internal battery and your phone’s requirements explains this gap.
Understanding Wh: The Real Energy Story
Wh stands for watt-hours, and this is where things get interesting. Watt-hours measure the actual energy stored in your battery – the total amount of work it can do. This gives you a much clearer picture of real-world performance.
One watt-hour means your battery can deliver one watt of power for one hour. Unlike mAh, Wh accounts for both current and voltage, making it the more accurate measure for comparing different batteries.
Why Wh Matters More for Power Stations
When you’re choosing a portable power station, Wh ratings tell you exactly how much energy you’re getting. A 500Wh power station will run a 50-watt device for 10 hours, regardless of the internal battery configuration.
This consistency makes Wh the preferred measurement for larger power systems. You won’t find many portable power stations advertised primarily by their mAh rating because it would be nearly meaningless without voltage information.
The Simple Conversion Formula
Converting between mAh and Wh requires one key piece of information: voltage. Here’s the basic formula you need:
Wh = (mAh × Voltage) ÷ 1000
The division by 1000 converts milliampere-hours to ampere-hours, which is necessary for the calculation to work correctly.
Step-by-Step Conversion Example
Let’s say you have a battery with these specifications:
- Capacity: 10000mAh
- Voltage: 3.7V
Using our formula: Wh = (10000 × 3.7) ÷ 1000 = 37Wh
This 10000mAh battery actually stores 37 watt-hours of energy. Now you can compare it accurately with other batteries.
Converting Wh Back to mAh
Going the other direction is equally simple:
mAh = (Wh × 1000) ÷ Voltage
If you have a 100Wh battery at 12V: mAh = (100 × 1000) ÷ 12 = 8333mAh
Real-World Battery Examples
Let me show you how these conversions work with actual devices you probably use every day.
Smartphone Batteries
A typical iPhone 14 has a 3279mAh battery at 3.8V. Converting to Wh: (3279 × 3.8) ÷ 1000 = 12.5Wh
This explains why a 20000mAh power bank doesn’t give you the 6+ charges you might expect. After accounting for conversion losses and voltage differences, you’re looking at 3-4 full charges in practice.
Laptop Batteries
Most laptops list their battery capacity in Wh because they operate at higher voltages. A MacBook Pro with a 70Wh battery at 11.4V would have: (70 × 1000) ÷ 11.4 = 6140mAh
That seems small compared to your phone’s 3000+ mAh rating, but the higher voltage means much more actual energy storage.
Electric Vehicle Comparison
Electric cars take this to the extreme. A Tesla Model 3 has about 75000Wh (75kWh) of battery capacity. At roughly 400V, that converts to about 187500mAh – but you’ll never see it advertised that way because the mAh number becomes meaninglessly large.
Portable Power Station Calculations
When shopping for portable power stations, you’ll almost always see Wh ratings prominently displayed. Here’s how to use that information effectively.
Estimating Runtime
Calculating how long a power station will run your devices is straightforward with Wh ratings:
Runtime (hours) = Power Station Wh ÷ Device Watts
A 500Wh power station running a 100W mini-fridge: 500 ÷ 100 = 5 hours of runtime
Multiple Device Calculations
Running several devices simultaneously? Add up their wattages first:
- LED light: 10W
- Laptop charging: 65W
- Phone charging: 15W
- Total: 90W
That same 500Wh power station would run all three devices for: 500 ÷ 90 = 5.6 hours
Efficiency Losses
Real-world performance is always lower than calculations suggest. I found through research that most power stations operate at 85-90% efficiency due to inverter losses and heat.
Build in a 10-15% buffer when planning your power needs. That 500Wh power station effectively provides about 425-450Wh of usable energy.
Common Conversion Mistakes
People make several predictable errors when working with battery calculations. Learning to spot these mistakes can save you from buying inadequate equipment.
Forgetting About Voltage
The biggest mistake is trying to compare mAh ratings across different voltages. A 10000mAh power bank at 3.7V stores much less energy than a 10000mAh battery pack at 12V.
Always convert to Wh for accurate comparisons. It’s the only way to make apples-to-apples comparisons between different battery technologies and configurations.
Ignoring Conversion Losses
Your power station might have 1000Wh of storage, but you won’t get 1000Wh out of it. Power conversion from DC to AC creates heat and wastes energy.
USB ports are more efficient than AC outlets, typically losing only 5-10% compared to 15-20% for AC conversion. Plan accordingly based on how you’ll actually use the power station.
Mixing Up Units
Watch out for manufacturers who list capacity in Ah (ampere-hours) instead of mAh. 1 Ah equals 1000 mAh, so a 100Ah battery is actually 100000mAh.
This commonly happens with larger batteries like those in RVs or boats. Always double-check the units before doing calculations.
Which Measurement Should You Use?
The answer depends on what you’re shopping for and how you plan to use it.
Use mAh When:
- Comparing similar devices at the same voltage
- Looking at phone batteries or small electronics
- Working with single-cell lithium-ion batteries
Use Wh When:
- Comparing different battery technologies
- Planning power consumption for camping or emergencies
- Shopping for portable power stations
- Calculating actual energy needs
Professional Recommendations
Industry experts consistently recommend focusing on Wh for anything larger than a smartphone. It eliminates confusion and gives you the information you actually need for planning purposes.
For portable power stations specifically, Wh ratings are your best friend. They tell you exactly how much energy you’re buying without any mathematical gymnastics required.
Battery Chemistry Differences
Different battery types operate at different voltages, which affects how mAh and Wh relate to each other.
Lithium-Ion Batteries
Standard lithium-ion cells operate at 3.6-3.7V nominal voltage. This is what you’ll find in most phones, laptops, and power banks. The voltage stays relatively stable throughout the discharge cycle.
Lead-Acid Batteries
Lead-acid batteries operate at 12V (nominal) and are common in cars, RVs, and backup power systems. Their higher voltage means fewer amp-hours are needed for the same energy storage.
LiFePO4 (Lithium Iron Phosphate)
LiFePO4 batteries operate at 3.2V per cell, slightly lower than standard lithium-ion. They’re becoming popular in power stations because they’re safer and last longer, even though they store slightly less energy per mAh.
Practical Shopping Tips
Armed with conversion knowledge, you can make much smarter buying decisions.
Compare Wh Per Dollar
Calculate the cost per watt-hour to find the best value. A $300 power station with 500Wh costs $0.60 per Wh. A $450 model with 1000Wh costs $0.45 per Wh – much better value.
Size vs. Capacity Trade-offs
Higher voltage batteries can pack more energy into smaller spaces. This is why laptop batteries seem small but last for hours, while your phone’s larger-looking battery dies faster under heavy use.
Temperature Considerations
Cold weather reduces battery capacity regardless of whether you measure in mAh or Wh. Lithium batteries can lose 10-20% capacity in freezing temperatures, something to consider for winter camping.
Conclusion
Understanding the difference between mAh and Wh empowers you to make informed decisions about portable power. While mAh measures current flow over time, Wh measures actual energy storage – the number that matters most for planning your power needs. Use the conversion formula (Wh = mAh × V ÷ 1000) whenever you need to compare batteries with different voltage ratings. For portable power stations and serious energy planning, focus on Wh ratings and remember to account for efficiency losses in your calculations. This knowledge will help you choose the right equipment and avoid disappointment when your devices don’t run as long as expected.
How do I know what voltage to use in the conversion formula?
Check the battery label, product specifications, or manual – voltage is usually listed as “nominal voltage” and represents the average operating voltage throughout the discharge cycle.
Why do power banks have different mAh ratings for input vs output?
Input ratings refer to the internal battery capacity, while output ratings account for conversion losses when charging your devices – output is always lower due to efficiency losses in the circuitry.
Can I use these formulas for car batteries too?
Yes, but car batteries are typically rated in Ah (not mAh) at 12V nominal voltage – a 100Ah car battery contains 1200Wh of energy using the same conversion principles.
What’s the difference between nominal and maximum voltage?
Nominal voltage is the average operating voltage during normal discharge, while maximum voltage is the peak when fully charged – always use nominal voltage for capacity calculations since it represents typical performance.
Do wireless charging pads affect these calculations?
Wireless charging is only about 70-80% efficient compared to wired charging, so your power station will drain faster when using wireless charging features – factor in this extra energy loss when planning runtime.
