Understanding Battery Capacity: mAh vs Wh Explained

Battery specs are confusing by design. A phone advertises 5,000 mAh. A laptop says 72 Wh. A power bank claims 26,800 mAh. Are these comparable? Not directly — and manufacturers exploit this confusion. Let's clarify.

mAh — Milliamp-Hours

mAh (milliamp-hours) measures electric charge — how many milliamps of current a battery can supply for one hour. A 5,000 mAh battery can theoretically supply 5,000 milliamps (5 amps) for one hour, or 1,000 milliamps (1 amp) for five hours, or 500 milliamps for ten hours.

mAh is used for phones, earbuds, smartwatches, and other small devices because it's a simple, large number that's easy to compare. Bigger mAh = longer battery life, right?

Not exactly. mAh only tells you half the story. It measures charge but ignores voltage.

Wh — Watt-Hours

Wh (watt-hours) measures energy — the total amount of work a battery can do. It combines charge AND voltage: Wh = (mAh × Voltage) / 1000.

A battery rated at 5,000 mAh and 3.7V contains: (5,000 × 3.7) / 1000 = 18.5 Wh of energy.

Wh is used for laptops, electric vehicles, and power stations because it's a more accurate measure of how much total energy is stored. When comparing batteries at different voltages, Wh is the only meaningful metric.

Why mAh Is Misleading for Power Banks

This is where the confusion gets exploited. A power bank advertises 26,800 mAh, and your phone has a 5,000 mAh battery. Simple math suggests the power bank should charge your phone about 5 times. But it won't — you'll get 3-4 charges at best.

Here's why: the power bank's internal battery runs at 3.7V, but USB output is 5V (or higher for fast charging). When converting 3.7V to 5V, energy is lost. The actual energy in the power bank:

26,800 mAh × 3.7V / 1000 = 99.16 Wh

Energy delivered at 5V (assuming 85% conversion efficiency):

99.16 Wh × 0.85 = 84.29 Wh usable

Your phone's battery: 5,000 mAh × 3.85V / 1000 = 19.25 Wh

Charges: 84.29 / 19.25 = approximately 4.4 charges

The Anker 737 Power Bank (24,000 mAh / 87.6 Wh) is one of the most efficient power banks we've tested, delivering close to its theoretical maximum in real-world use.

The Airline Battery Rule

Airlines restrict carry-on batteries to 100 Wh. This is why laptop batteries and large power banks list Wh prominently — it's a regulatory requirement.

A 27,000 mAh power bank at 3.7V = 99.9 Wh — just under the limit. This is not a coincidence. Manufacturers design their largest power banks to max out at just under 100 Wh.

Power banks over 100 Wh (up to 160 Wh) require airline approval. Over 160 Wh is prohibited on flights entirely.

The Baseus 65W Portable Charger at 20,000 mAh (74 Wh) is a sweet spot for travel — well under the airline limit with enough capacity for a full laptop charge plus several phone charges.

Read our power bank buying guide →

How to Compare Batteries Properly

Same Device Category (phone vs. phone)

mAh works fine for same-category comparisons because the battery voltage is nearly identical across all phones (3.7-3.87V). A 5,000 mAh phone has about 25% more capacity than a 4,000 mAh phone. This comparison is valid.

Different Device Categories (phone vs. laptop vs. power bank)

Use Wh. Always. A laptop with a 72 Wh battery stores about 4x more energy than a phone with an 18.5 Wh battery — but it also consumes far more power, which is why laptops and phones have similar battery life despite vastly different capacities.

Power Consumption Matters More

Battery capacity tells you how much energy is stored. Battery life depends on how quickly that energy is consumed. A 5,000 mAh phone with an efficient processor and a 1080p display will outlast a 5,500 mAh phone with a power-hungry chip and a 1440p display.

This is why Apple iPhones consistently deliver excellent battery life despite having smaller mAh batteries than competing Android phones — Apple optimizes the entire stack (chip, display, software) for power efficiency.

Battery Degradation

All lithium batteries lose capacity over time. After 500 full charge cycles, most batteries retain 80% of their original capacity. After 1,000 cycles, it's typically 70-75%.

A 5,000 mAh phone battery after two years of heavy use might effectively be a 4,000 mAh battery. This is normal and unavoidable with current lithium chemistry.

Tips to minimize degradation:

• Avoid keeping the battery at 100% for extended periods
• Don't let it drain to 0% regularly
• Avoid charging in extreme heat
• Use optimized charging features (both iOS and Android offer these)

The Anker Prime 20,000 mAh Power Bank has a smart charging system that helps manage its own internal battery health for longevity.

Portable Power Stations — The Big Batteries

Portable power stations are measured in Wh because their capacities are so large that mAh numbers would be absurdly high. A 500 Wh power station is equivalent to roughly 135,000 mAh at 3.7V — that number is meaningless to consumers.

Wh directly tells you what you can run:

• 500 Wh charges a laptop (72 Wh) about 6 times
• 500 Wh runs a 50W appliance for about 10 hours
• 1000 Wh runs a mini fridge for about 10-15 hours

The EcoFlow RIVER 2 Max at 512 Wh is an excellent portable power station for camping, tailgating, or emergency backup. The Jackery Explorer 1000 Plus at 1264 Wh handles heavier loads and can be expanded with additional battery packs.

Quick Reference

| mAh | Voltage | Wh | Typical Device | |-----|---------|-----|----------------| | 500 | 3.7V | 1.85 | Wireless earbuds | | 2,000 | 3.7V | 7.4 | Smartwatch | | 5,000 | 3.85V | 19.25 | Smartphone | | 20,000 | 3.7V | 74 | Power bank (travel) | | 26,800 | 3.7V | 99 | Power bank (max airline) | | N/A | N/A | 50-100 | Laptop battery | | N/A | N/A | 300-2000 | Portable power station |

When in doubt, compare in Wh. It's the only unit that gives you a true apples-to-apples energy comparison.

Compare our top-rated power banks and portable chargers →

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