mAh vs Wh: Understanding Power Bank Capacity Before You Import

Shenzhen Istyle Technology • October 8, 2026 • 8 min read

Pick up any power bank spec sheet and you will find two capacity numbers: mAh and Wh. Buyers quote mAh on the packaging because it looks big, but airlines, customs and certification labs care about Wh. Confusing the two is one of the most common — and most expensive — mistakes importers make. This guide explains what each number actually measures, how to convert between them, and what to verify before you place an order with a factory.

What mAh really tells you

mAh stands for milliampere-hour. It measures how much charge a battery can deliver at a given voltage over time. It is a useful marketing number because it is large and easy to compare — 10,000mAh, 20,000mAh, 30,000mAh — but on its own it does not tell you how much energy the battery holds.

The catch: mAh is quoted at the cell's nominal voltage (roughly 3.7V for the lithium cells inside most power banks). When you actually charge your phone, the output is delivered at 5V or higher. Energy is voltage-dependent, so a mAh figure without a voltage is an incomplete statement. That is why two power banks with the same 10,000mAh can behave very differently in real use.

What Wh really tells you

Wh stands for watt-hour and is a direct measure of energy — the number regulators and carriers use to classify lithium batteries. Unlike mAh, Wh is voltage-independent in the sense that it already accounts for voltage, so it compares fairly across products and chemistries.

If you have ever filled out a shipping form asking for the battery's watt-hour rating, you have already met the number that matters most to logistics. The full energy a power bank stores, and the amount of lithium it contains, is expressed in Wh.

The conversion: mAh to Wh

The formula connecting the two is simple:

Wh = (mAh ÷ 1000) × V

For a typical lithium power bank cell, V (nominal voltage) is about 3.7V. So a 10,000mAh cell is roughly 37Wh, a 20,000mAh cell is roughly 74Wh, and a 30,000mAh cell crosses 110Wh. Run these numbers on any model you are considering, and the "big" mAh figure suddenly becomes a manageable, comparable energy rating.

Note that the voltage you use matters. If a supplier quotes mAh at 3.7V and another quotes the same product at 5V output, the raw mAh figures will differ even though the stored energy is identical. Always ask at which voltage the mAh was measured — a professional spec sheet states it explicitly.

Why 100Wh is the number airlines care about

Air transport rules classify lithium-ion batteries by watt-hours. Batteries under 100Wh — which covers most 10,000mAh and 20,000mAh power banks — are treated as the standard category for passenger carry-on and for most courier and air-freight shipments. Units between 100Wh and 160Wh face tighter limits and carrier approval. Above 160Wh, lithium-ion batteries are generally restricted from passenger aircraft.

The practical takeaway for importers: if your target market involves air travel accessories, keeping the rating under 100Wh removes a whole layer of friction. And whichever model you choose, the Wh figure — not the mAh figure — is what your UN38.3 test report and transport documents will state. Mismatched capacity numbers between your packaging and your certification paperwork is exactly the kind of discrepancy that stalls a shipment at customs.

Marked capacity vs rated (usable) capacity

The capacity printed on the box is the cell's marked capacity. The amount that actually reaches your customer's phone is the rated capacity, and it is always lower because energy is lost to voltage conversion, heat and circuitry. Reputable suppliers publish both numbers and label the rated capacity with the output conditions used to measure it.

This is why a 10,000mAh power bank will not deliver 10,000mAh to a phone. It is not a defect — it is physics. Be skeptical of any listing that shows only one number with no conditions attached. If you understand the cell, you understand the loss: see our guide to power bank battery cells for how cell choice shapes real-world performance.

How to read a spec sheet before you order

• Cell rated capacity & voltage — e.g. 10,000mAh @ 3.7V, which you can convert to Wh yourself.
• Rated output capacity — the usable number, with the test conditions stated.
• Wh rating — confirm it matches the UN38.3 report and shipping documents.
• Input / output ports — check they match your market's devices.
• Certifications — CE / RoHS for the EU, FCC for the US, UN38.3 for transport.

A quick capacity checklist

• ☐ Both mAh and Wh stated on the spec sheet
• ☐ Voltage at which mAh was measured is specified
• ☐ Rated (usable) capacity published with test conditions
• ☐ Wh rating consistent across packaging, spec sheet and UN38.3 report
• ☐ Capacity figure matches the sample you actually test

Getting the capacity right at the spec stage saves problems at every stage after it — certification, shipping, retail and warranty. We are Shenzhen Istyle Technology, a power bank OEM/ODM manufacturer with CE / FCC / RoHS / UN38.3 coverage on our standard range, samples shipped in 3–5 days, and standard production in 15–25 days.

See real capacity options on our products page, explore OEM / ODM customization, or send us your requirements for a quote — WhatsApp and email both work.

More from the Istyle blog: all articles • Certifications & shipping compliance • OEM & ODM service