By Garrett BradfordWhen you shop for portable battery power for camping, you see two common capacity ratings: milliamp-hours (mAh) and watt-hours (Wh). While mAh is widely used for smaller power banks, it can be misleading because it does not account for voltage. Watt-hours tell you the actual energy stored, making it the better measure for comparing batteries of different voltages. This article explains the difference, shows you how to convert between them, and covers why Wh matters for airline travel and for choosing between a power bank and a larger power station.
Understanding Watt-Hours and Milliamp-Hours
Milliamp-hours (mAh) measure electric charge. One milliamp-hour means the battery can deliver one milliamp of current for one hour. To get a sense of total energy, you must multiply by voltage. Watt-hours (Wh) measure energy directly. The formula is simple:
Watt-hours = Volts × Amp-hours
Since 1 amp-hour (Ah) equals 1,000 milliamp-hours (mAh), you can convert mAh to Ah by dividing by 1,000. Then multiply by the battery’s voltage to get watt-hours.
For example, a power bank rated at 20,000 mAh at its internal cell voltage of 3.7 volts holds 20 Ah × 3.7 V = 74 Wh of raw energy. A power station that lists 300 Wh directly already accounts for its battery voltage (often 12 V or higher). Without voltage, the mAh number alone cannot tell you how much work the battery can do.
Why mAh Alone Is Misleading
Consider two camping batteries: a small power bank and a larger portable power station. The power bank might advertise 20,000 mAh. The power station might also advertise 20,000 mAh, but at a much higher voltage, such as 12 V. The power station would then hold 20 Ah × 12 V = 240 Wh, more than three times the energy of the power bank. Yet both show the same mAh number. If you only look at mAh, you would incorrectly think they have similar capacity.
This is why you should always compare batteries using watt-hours. For camping, you need to know how long a device can run. A fan that draws 10 watts will run for 7.4 hours on the 74 Wh power bank (before conversion losses) but for 24 hours on the 240 Wh power station. The mAh label alone does not reveal that difference.
Another common scenario: power banks often use 3.7 V lithium-ion cells internally, but they output 5 V USB. The conversion from 3.7 V to 5 V involves a boost converter, which has efficiency losses. So the usable watt-hours at the USB port are lower than the raw cell energy. This further complicates comparisons based solely on mAh.
Converting mAh to Wh: A Worked Example
Let’s walk through a typical conversion for a power bank you might take camping. Assume the power bank is rated at 20,000 mAh and uses 3.7 V cells. The raw energy is:
20,000 mAh ÷ 1,000 = 20 Ah
20 Ah × 3.7 V = 74 Wh
That 74 Wh is the energy stored in the cells. However, when you charge a phone or a camping light through the USB port, the power bank’s internal circuitry converts the battery voltage to 5 V. This step is not 100% efficient. A common efficiency range for USB boost converters is 85–90%. Using 85% as a conservative example:
Usable Wh at USB output = 74 Wh × 0.85 ≈ 63 Wh
So from a 20,000 mAh power bank, you can expect roughly 63 watt-hours available to your devices. If you are charging a phone with a 10 Wh battery, you could fully charge it about six times (63 ÷ 10 ≈ 6.3), accounting for some losses in the phone’s charging circuit as well.
For a larger power station that lists 300 Wh, the number already reflects the energy after the battery’s internal voltage is accounted for. But if you use the AC inverter to power a 120 V appliance, you will lose another 10–15% in the inversion step. So the usable AC watt-hours might be around 255–270 Wh.
Always check the manufacturer’s specifications for rated capacity and any efficiency notes. Some brands list “rated capacity” at the output voltage, which can help you compare more fairly.
Comparing a Power Bank and a Power Station Using Watt-Hours
When you are deciding between a small power bank and a larger portable power station, watt-hours give you an apples-to-apples comparison. A typical power bank for camping might hold 74 Wh (20,000 mAh at 3.7 V). A mid-range power station might hold 300 Wh. That is about four times the energy, but the power station also provides AC outlets, higher USB power, and often solar charging input.
To see how far each can go, consider common camping devices. A phone charger draws about 10 watts. On the 74 Wh power bank (63 Wh usable), you could run a phone charger for about 6.3 hours. On the 300 Wh power station (255 Wh usable after inverter losses), you could run it for about 25.5 hours. For a small 12 V cooler that draws 40 watts, the power bank cannot power it directly (no 12 V output), but the power station could run it for about 6.4 hours (255 ÷ 40).
If you need to power larger appliances like a laptop, a CPAP machine, or a portable refrigerator, a power station with a higher watt-hour rating is usually the better choice. You can browse watt-hour and amp-hour explanations to understand how capacity relates to run time for specific devices. For a list of typical power draws, see the camping appliance wattage chart.
When comparing models, look for the watt-hour rating on the spec sheet. If only mAh is given, you can calculate Wh as shown above, but be aware that the voltage used in the calculation may not be the output voltage. For power stations, the battery voltage is often 12 V, 24 V, or higher, and the manufacturer usually lists Wh directly. For power banks, the internal cell voltage is typically 3.7 V, but some newer models use higher voltage cells (like 7.4 V) to improve efficiency. Always check the label.
If you are ready to choose a power station for your camping trips, consider models that list watt-hours clearly. You can compare portable power stations by their watt-hour ratings to find one that matches your energy needs.
Airline Travel Limits: Why Watt-Hours Matter
If you fly to your camping destination, you must follow airline and FAA rules for lithium batteries. The FAA limits carry-on lithium-ion batteries to 100 watt-hours per battery without special approval. Batteries between 100 and 160 watt-hours may be allowed with airline approval. Batteries over 160 watt-hours are generally prohibited in carry-on and checked baggage.
These limits are expressed in watt-hours, not mAh. A power bank labeled 20,000 mAh at 3.7 V equals 74 Wh, which is under the 100 Wh limit and allowed in carry-on. But a 50,000 mAh power bank at 3.7 V equals 185 Wh, which exceeds the limit and would not be allowed. Some power banks list mAh at the output voltage (5 V), which can be misleading. For example, a 20,000 mAh power bank at 5 V output would be 100 Wh, but the internal cells are still 3.7 V, so the actual energy is 74 Wh. Airlines typically use the internal cell voltage to calculate Wh. Check the manufacturer’s labeling for the Wh rating or the voltage used.
For power stations, the Wh rating is usually printed on the unit or in the manual. Most camping power stations hold well over 160 Wh, so they generally cannot go on a plane in either carry-on or checked bags; only small units fall under the limits. You can check the FAA PackSafe lithium batteries page for current guidelines. Always verify with your airline before traveling, as policies can vary.
To avoid surprises, always look for the watt-hour rating on the battery or its packaging. If only mAh is given, calculate Wh using the battery’s nominal voltage (usually 3.7 V for lithium-ion cells). If the result is near the limit, consider a smaller battery or check with the airline.
How to Find the Watt-Hour Rating on Your Device
Most camping batteries and power stations list the watt-hour rating on the label, in the user manual, or on the manufacturer’s website. For power banks, look for a small line of text that says “Wh” or “watt-hours.” It may be printed near the mAh rating. If you cannot find it, you can calculate it:
- Find the battery’s voltage (often 3.7 V for lithium-ion power banks, but check the label).
- Convert mAh to Ah by dividing by 1,000.
- Multiply Ah by voltage to get Wh.
For power stations, the Wh rating is almost always listed prominently because it is the standard measure for larger batteries. If you see only amp-hours (Ah) at a specific voltage, multiply Ah by voltage to get Wh. For example, a power station rated 25 Ah at 12 V holds 300 Wh.
Keep in mind that some manufacturers advertise “equivalent” capacities based on output voltage, which can inflate the number. Stick to the internal cell voltage or the rated Wh as stated by the manufacturer for a fair comparison.
FAQ
What does mAh stand for and how is it different from Wh?
mAh stands for milliamp-hours, a measure of electric charge. Wh stands for watt-hours, a measure of energy. Because energy depends on voltage, mAh alone cannot tell you how much power a battery can deliver. Wh accounts for voltage, making it the correct measure for comparing batteries of different voltages.
How do I convert mAh to Wh for a power bank?
Divide the mAh by 1,000 to get amp-hours (Ah). Then multiply by the battery’s nominal voltage (usually 3.7 V for lithium-ion power banks). For example, 20,000 mAh ÷ 1,000 = 20 Ah; 20 Ah × 3.7 V = 74 Wh. Remember that after conversion to USB output, you lose some energy to heat (typically 10–15%).
Can I take a 50,000 mAh power bank on a plane?
It depends on the voltage. A 50,000 mAh power bank at 3.7 V equals 185 Wh, which exceeds the FAA’s 100 Wh limit for carry-on without approval. Most airlines will not allow it. Check the watt-hour rating on the label, and if it is over 100 Wh, you may need special permission. Always verify with your airline and the FAA guidelines.
Why do power stations list Wh while power banks list mAh?
Power stations typically have higher voltages (12 V, 24 V, etc.) and larger capacities, so Wh is the standard industry measure. Power banks often use 3.7 V cells and are marketed with mAh because consumers are familiar with that number. However, for accurate comparison, you should convert to Wh or look for the Wh rating on the power bank’s label.
Closing Thoughts
Understanding the difference between watt-hours and milliamp-hours helps you choose the right camping battery for your needs and avoid surprises at the airport. Always compare batteries by their watt-hour rating, especially when mixing power banks and power stations. Use the conversion formula to check any battery’s true energy capacity, and remember that conversion losses reduce the usable power. For more on how battery capacity relates to running your gear, read about running watts vs surge watts and consult the camping appliance wattage chart to estimate run times. With watt-hours as your guide, you can confidently power your camping adventures.
About Garrett Bradford
Garrett covers off-grid power for camping, rv & vanlife, comparing specs, features and long-term owner feedback to help readers choose with confidence.
