If you source power banks or portable power stations from China to sell overseas, you’ve likely noticed something confusing: the same product prints “10,000mAh” on the box, and elsewhere lists a “rated capacity of 6,500mAh” — nearly a 40% gap between the two numbers. Many buyers’ first instinct is “this must be a fake capacity claim” — but that judgment is often wrong, and can lead you to wrongly flag legitimate products while missing the ones that actually have a problem. This article explains which “capacity shrinkage” is normal physics, which is real fraud, and how to verify.
1. Shrinking to roughly 60-70% is normal voltage conversion loss — not fraud
The lithium cell inside a power bank is typically rated around 3.7V, but output to charge a device requires stepping up to the standard 5V — this voltage conversion inherently loses energy; it’s physics, not a manufacturer lying to you.
Do the math: for a cell rated at 10,000mAh, the theoretical maximum output = 10,000mAh × 3.7V ÷ 5V = 7,400mAh — already 26% below the label, and that’s the theoretical figure assuming zero real-world loss. Add realistic circuit conversion efficiency (typically 75-90% for legitimate products), and a final rated capacity landing at 60-70% of the labeled cell capacity is completely normal.
Real examples: Ugreen’s 10,000mAh power bank has a rated capacity of 6,500mAh (5V/3A); Xiaomi’s 10,000mAh power bank rates at 5,800mAh (5V/4A) — both mainstream, reputable brands, both landing right around “60%.” Shanghai’s Administration for Market Regulation once tested a Huawei 20,000mAh power bank and found a conversion efficiency of 92.7% — an exceptionally strong result, but it also confirms that “rated capacity differs from labeled cell capacity” is standard industry practice, not evidence of fraud.
2. Real fraud hides in the cell capacity number itself
This distinction matters: the “shrinks to 60%” pattern above assumes the underlying cell capacity is genuine. Real fraud happens when a manufacturer substitutes lower-capacity cells while labeling them as if they were higher-capacity — making the starting “cell capacity” number itself false.
A real teardown case: a power bank labeled “12,000mAh cell capacity” was opened to reveal only 4 18650 cells inside; based on the labeled figure, each cell should individually deliver 3,000mAh — but 3,000mAh 18650 cells are only achievable by a handful of top-tier international manufacturers, at significant cost. Actual testing found the cells averaged only 2,068mAh each — nearly a third short of the claimed 3,000mAh. Worse, the cells carried no manufacturer identification at all, making the source untraceable if something went wrong.
3. An official statistic you can cite directly: only a 63.3% pass rate
Shanghai’s Administration for Market Regulation conducted a spot check of power bank products in local production and circulation — of 30 batches tested, only 19 passed, a 63.3% pass rate. This tells you the quality issues in this category aren’t a rare edge case — a meaningful share of products genuinely have problems, and it’s worth taking seriously during sourcing.
4. Specific verification methods you can use
- Require the supplier to label both “cell capacity” and “rated capacity” together, with the tested output condition noted (e.g., 5V/3A). A single flashy large number with no voltage or rated-capacity information is a red flag.
- Use weight as a rough sanity check. A genuine 10,000mAh-class lithium cell weighs roughly 200g. If a “30,000mAh” power bank weighs less than your phone, that number is very likely wrong.
- Be wary of claims that exceed physical limits. Listings for “400,000mAh” power banks have appeared on the market — converted to watt-hours (400,000mAh × 3.7V ÷ 1,000 = 1,480Wh), that’s more energy than most stationary outdoor power stations (a Jackery 1000, for comparison, holds about 1,002Wh). No mainstream brand’s handheld USB-C power bank achieves this figure — such claims are almost always either outright fabrication, or a trick using the 5V output voltage instead of the standard 3.7V cell voltage to inflate the mAh number by roughly 35% while the actual stored energy stays identical.
- Cross-check the watt-hour figure on the UN38.3 transport certification report against the product’s converted claimed capacity (see our battery sourcing guide) — this is a third-party document that’s harder to falsify than marketing copy on the packaging.
- Understand the relationship between airline limits and product positioning: power banks rated at 100Wh or below can be carried on flights without restriction; 100–160Wh requires airline approval; over 160Wh is prohibited. This is why “20,000mAh” is such a common sweet spot in the market (it converts to just under 100Wh), while products above “30,000mAh” often need explicit flight-compliance disclosure.
The bottom line
A power bank’s “rated capacity landing at roughly 60% of the labeled cell capacity” is a normal consequence of voltage conversion physics, not evidence of fraud — even mainstream brands like Ugreen, Xiaomi, and Huawei land in this same range. What actually deserves scrutiny is whether the cell capacity number itself has been faked, by substituting lower-capacity cells. A Shanghai regulator’s 63.3% pass rate is a reminder that real quality problems do exist in this category at a meaningful rate — but the right way to catch them isn’t judging by the “rated ÷ labeled” ratio alone. It’s requiring dual labeling, cross-checking the UN38.3 watt-hour figure, and staying alert to claims that exceed physical limits.
Voltage conversion figures and efficiency ranges reflect standard lithium-ion power bank engineering as documented across multiple industry and consumer-testing sources as of 2026. The Shanghai regulatory spot-check figure (63.3% pass rate) is drawn from official Administration for Market Regulation reporting. Verify specific capacity claims and certification documents for your own product before making sourcing decisions. General guidance, not legal or safety advice.