Product Claims Investigation
The short answer. No, and the makers' own figures say so. On the four listings where the claim can be checked against a phone maker's published battery size, a 20,000mAh power bank puts between 14,500mAh and 15,160mAh into the phone: 72.5% to 75.8% of the number on the box.
We call this the three-quarter rule: expect about three-quarters of a power bank's headline mAh to reach your phone. It is not a fault and not a false claim. The 20,000mAh describes the cells inside, measured at a lower voltage than the one your phone is charged at.
Research carried out 31 October 2026, published 1 November 2026. Desk research only: Look Into has not handled or measured these power banks. Every figure is the maker's own, or arithmetic on the maker's own figures.
Prices and specs last checked by Look Into on 31 October 2026 · next check 29 January 2027 · how we picked
The claim being investigated
- The claim
- "20,000mAh", in the title of all 20 listings we read.
- What most shoppers take it to mean
- That the pack can put 20,000mAh into a phone, so it will charge a 5,000mAh phone four times.
- What it actually describes
- The capacity of the lithium-ion cells inside, at their own nominal voltage of about 3.6V to 3.7V.
- Verdict
- A cell rating, not a measure of what reaches your phone, and none of the listings says so. We could not check the cells themselves.
What 20,000mAh actually means
A milliamp-hour figure means nothing on its own: it has to be read with a voltage. The cells in a power bank sit at about 3.7V. USB output starts at 5V. The same stored energy is fewer milliamp-hours at the higher voltage, before anything is lost in the conversion.
Calculated 20,000mAh × 3.7V = 74Wh of energy in the cells.
Calculated 74Wh ÷ 5V = 14,800mAh at USB voltage, if nothing were lost.
Maker's figure Anker says good boost converters run at about 85% to 90% efficiency, which takes that to 12,580mAh to 13,320mAh at 5V.
Voltage and efficiency figures from Anker's own explainer, Why your 10,000mAh power bank isn't actually 10,000mAh (dated 20 July 2026, read 31 October 2026), which gives a 10,000mAh pack an actual capacity of 6,000mAh to 6,500mAh.
Your phone then stores that energy at its own battery voltage, close to the power bank's cell voltage, which is why the charge counts below come out higher than the 5V figure. Two different milliamp-hours are in play, and listings never say which one they mean.
The evidence: what the makers' own charge counts imply
Ten of the 20 listings say in their title or bullet points how many times the pack will charge a named phone. Apple does not publish iPhone battery capacity on its specifications pages, so iPhone counts cannot be checked against a maker figure. Samsung does publish it, so these four can.
| Power bank (20,000mAh) | Listing's own claim | Samsung's stated battery | mAh into the phone | Share of 20,000mAh |
|---|---|---|---|---|
| Anker Zolo 30W | Galaxy S24, 3.79 times | 4,000mAh | 15,160mAh | 75.8% |
| CUKTECH 45W | Galaxy S24 Ultra, 2.9 times | 5,000mAh | 14,500mAh | 72.5% |
| UGREEN Nexode 45W | Galaxy S25 Ultra, 3 times | 5,000mAh | 15,000mAh | 75.0% |
| UGREEN Nexode 20W | Galaxy S24 Ultra, 3 times | 5,000mAh | 15,000mAh | 75.0% |
Charge counts from each Amazon UK listing's bullet points, read 31 October 2026. Battery sizes are Samsung UK's "Battery Capacity (mAh, Typical)" for the Galaxy S24 (4,000mAh), S24 Ultra (5,000mAh) and S25 Ultra (5,000mAh), read 31 October 2026. "mAh into the phone" is the charge count multiplied by that battery size.
Four makers, three brands, a spread of 3.3 percentage points. Whatever losses each design has, the makers' own marketing lands every one of them close to three-quarters.
What the listings tell you, and what they leave out
We read the first 20 unsponsored Amazon UK results for "20000mah power bank" on 31 October 2026, in two scopes: the title and bullet points a shopper sees first, then everything the seller wrote, including the description, the brand content and the product details table.
- 20 of 20 put 20,000mAh in the title.
- 0 of 20 state a rated or output capacity in text, in either scope.
- 0 of 20 state the cell voltage behind the mAh figure.
- 1 of 20 gives a watt-hour figure, and only outside the bullet points: UGREEN's 20W Nexode lists 72Wh, which is 20,000mAh at 3.6V rather than 3.7V.
- 10 of 20 give a phone charge count in the title or bullets; an eleventh, Belkin's UltraCharge, gives one only in its comparison table.
Rated capacity is usually printed on the power bank itself and often shown in listing photos. Text in an image is not something a shopper can search or a screen reader can read, and we did not count it.
| Listing | Headline | Rated capacity in text | Watt-hours in text | Phone charge claim (title or bullets) |
|---|---|---|---|---|
| Amazon Basics High-Capacity Portable Charger, 20,000mAh ASIN B0FFM4BY6C | 20,000mAh | No | No | None |
| Anker Zolo Power Bank, 20,000mAh 30W ASIN B0CZ9LH53B | 20,000mAh | No | No | iPhone 15 up to 4 times; Samsung S24 3.79 times |
| xielaobam 20000mAh 22.5W, LCD display ASIN B0HDS8ZN8B | 20,000mAh | No | No | None |
| UGREEN Nexode 45W 20,000mAh ASIN B0DSPVDYQ9 | 20,000mAh | No | No | 3 full charges for Galaxy S25 Ultra; 4.2 for iPhone 16 |
| Anker Power Bank 20,000mAh 45W, dual built-in cables ASIN B0DSZKKJTK | 20,000mAh | No | No | 4 full charges for an iPhone 16 |
| INIU 20000mAh 45W ASIN B0DCZ82MGG | 20,000mAh | No | No | 4 charges for phones or 2 for tablets |
| yixiugo 20000mAh 22.5W, built-in cables ASIN B0H45GG7JF | 20,000mAh | No | No | None |
| CUKTECH 45W 20000mAh ASIN B0D8KH4LNB | 20,000mAh | No | No | iPhone 15 up to 3.9 times; Samsung S24 Ultra 2.9 times |
| VRURC 20000mAh 22.5W ASIN B099F29H7Y | 20,000mAh | No | No | None |
| Xiaocodou 20000mAh PD20W, LCD display ASIN B0DPQ84CQT | 20,000mAh | No | No | None |
| Anker Power Bank 20,000mAh 87W ASIN B0CXDXP8VR | 20,000mAh | No | No | None |
| Charmast 22.5W 20000mAh, 4 cables ASIN B0CJBQBB7F | 20,000mAh | No | No | iPhone 15 up to 4 times |
| zaoziron 20000mAh 22.5W, 2 cables ASIN B0FCLL8KGB | 20,000mAh | No | No | None |
| VEGER 20000mAh ASIN B0F678XXKT | 20,000mAh | No | No | None |
| UGREEN Nexode 20,000mAh PD 20W ASIN B0CSSRD4NT | 20,000mAh | No | Yes, 72Wh | iPhone 15 Pro up to 4.5 times; Galaxy S24 Ultra 3 times |
| Belkin BoostCharge 20000mAh 15W ASIN B09NTNTVRJ | 20,000mAh | No | No | None |
| Sprockly 20000mAh 22.5W, 3 cables ASIN B0H9XSYR51 | 20,000mAh | No | No | up to 3 full charges for iPhone 16 |
| IAIGG 20000mAh mini ASIN B0D8HVKC1F | 20,000mAh | No | No | most smartphones more than 2.5 times |
| INIU 20000mAh 65W laptop power bank ASIN B0DB89DSHV | 20,000mAh | No | No | 1 full charge for a MacBook Air; over 3 for flagship phones |
| Belkin UltraCharge 20000mAh 45W ASIN B0GXBYB3WB | 20,000mAh | No | No | Only in the comparison table: 3.8 charges (iPhone 17 Pro), in the comparison table only |
Listings in the order Amazon UK returned them, sponsored results excluded, read 31 October 2026. A missing figure is a gap in the listing, not evidence that the product falls short.
Work out what your phone will get
Enter the power bank's headline capacity and your phone's battery size. The range uses the 72.5% to 75.8% implied by the four checkable claims above.
What this means if you are buying one
- Divide by your phone's battery and multiply by about three-quarters. A 20,000mAh pack is about three full charges of a 5,000mAh phone, not four.
- Compare power banks on watt-hours when a maker gives them. Watt-hours are the same at any voltage, which is why airlines use them: our power banks guide sets out the 100Wh hand-luggage limit.
- Treat a charge count as the maker's estimate for a named phone. It is more useful than the mAh headline, but none of the listings say how it was measured.
What this investigation could not check
- We did not measure any power bank. The three-quarter figure comes from the makers' own claims, so it shows what makers expect, not what a unit delivers on test.
- Six of the ten charge counts name only iPhones, unnamed "phones" or a MacBook Air of unstated model. Apple does not publish iPhone battery capacity, so those six cannot be checked.
- Typical battery capacity, the figure Samsung publishes, can sit slightly above the rated minimum. Using it makes the implied share slightly higher, not lower.
- Rated capacity printed on the case or in listing images was not read. A listing may show it in a photo.
- Results for a different search, or on another day, will differ.
How we did it
Maker's claim Headlines, charge counts and watt-hours as written on each listing. Maker's figure Phone battery sizes from Samsung UK; conversion efficiency from Anker. Calculated Everything else, shown above. Independent testing None used. Look Into testing None.
This investigation follows Look Into's investigation standards: dated samples, labelled evidence, full working and a right of reply for any company named.
Sources
- Amazon UK search results and the 20 product listings named above, read 31 October 2026.
- Samsung UK specifications: Galaxy S24, Galaxy S24 Ultra, Galaxy S25 Ultra, read 31 October 2026.
- Apple UK, iPhone 16 technical specifications: battery listed by playback hours, no capacity, read 31 October 2026.
- Anker, Why your 10,000mAh power bank isn't actually 10,000mAh, dated 20 July 2026, read 31 October 2026.
Change log
- 1 November 2026: first published, on listings and specifications read 31 October 2026.
This page carries no affiliate links and earns Look Into nothing. If you want to buy one, our power banks guide carries picks, and it does use affiliate links.