A 20,000mAh power bank does not give you 20,000mAh. It gives you about 14,000, and the company that makes the cells will tell you so if you read their support pages instead of their product page.
The 70% rule, straight from the manufacturer
Anker publishes the formula on its own site: usable charges = (power bank capacity x 0.7) / device battery capacity. The 0.7 is the conversion loss — the cells inside run at about 3.7 volts and your phone charges at 5, 9 or 20, and every step up costs energy as heat.
So a 20,000mAh pack is roughly 14,000mAh of delivered charge. Against an iPhone 15 Pro at 3,274mAh that is about 4.27 charges, which matches the “about 4 times” claim on every listing. The number is not a lie; it is a different number than the one on the front of the box, and knowing the difference is how you stop being disappointed.
The second number almost nobody publishes is the recharge time, and it is the one that decides whether the pack is useful. Anker states roughly 5 hours 12 minutes for a 20,000mAh unit on a 20W-or-higher charger — meaning the pack’s input wattage, not its output, is what stands between you and a full battery.
| Anker 20,000 30W (A1384) | INIU 65W | INIU 45W | |
|---|---|---|---|
| Published capacity | 20,000 mAh | 20,000 mAh class | 20,000 mAh class |
| Max output | 30 W single USB-C | 65 W (laptop-class) | 45 W |
| Ports | 3 (2 USB-C + 1 USB-A) | Per listing | Per listing |
| Total with two devices | 24 W | Not published in bullets | Not published in bullets |
| Wh (approx, 3.7 V cell) | 74 Wh | 74 Wh | 74 Wh |
| Size / weight | 151 x 71 x 28 mm, 485 g | Per listing | Per listing |
| Recharge time | About 5 h 12 m on a 20 W+ charger | Faster input on higher-watt models | Faster input on higher-watt models |
| Price | See button | See button | See button |
All three sit around 74 watt-hours, which is comfortably under the 100Wh carry-on limit most airlines apply — the practical ceiling for a pack you can fly with is about 27,000mAh at 3.7 volts. Above that you need airline approval, and no amount of “travel” in the marketing changes it.
1. Anker 20,000 30W (A1384): the documented one
Two USB-C and one USB-A, 30W on a single USB-C port, 18W on USB-A, and a total of 24W when two outputs are active. That last figure is the honest one: with a phone and a tablet plugged in together, you are charging at 24W split between them, not at 30W each. 151 x 71 x 28 mm, 485 g, with an LED readout of remaining charge.
Thirty watts is a phone-and-tablet number, not a laptop number. It will top up a MacBook Air slowly and will not keep a 14-inch Pro alive under load.
Buy it if you charge phones, earbuds, and a tablet, and you want a pack whose limits are published. Skip it if a laptop is on the list.
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2. INIU 65W: the laptop-class one
Sixty-five watts is the threshold where a power bank stops being a phone accessory and starts being a laptop charger. That is the entire argument for this one: same 20,000mAh class, same ~74Wh, but the output can hold a thin laptop at working speed rather than trickling into it.
The catch with any high-watt pack is heat. Delivering 65W from a pocket-sized cell pack means the electronics run warm, and the failure reports in this category are almost always thermal rather than capacity. Check that the listing publishes a temperature or protection spec before you buy.
Buy it if you work off a laptop away from outlets. Skip it if you only charge phones — the extra watts buy nothing.
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3. INIU 45W: the middle
Forty-five watts is enough for a MacBook Air at full speed and enough for most tablets, which makes it the sane compromise if you want laptop capability without paying for 65W. It is also where the price curve flattens: the jump from 30W to 45W buys real capability, the jump from 45W to 65W mostly buys a heavier pack.
Buy it if your laptop is Air-class or you mostly travel with a tablet. Skip it if you need to run a Pro laptop at load.
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The short version
Multiply the mAh by 0.7 to get what you can actually use, check the watt-hours against the 100Wh airline line, and check the input wattage because that sets how long the pack spends refilling. Then choose output: 30W for phones and tablets, 45W for an Air, 65W if a Pro laptop has to keep working.