01What does mAh mean, exactly?
mAh means milliamp-hours. It's the amount of electric charge a battery can deliver: a 1,000 mAh battery could, in theory, supply 1,000 milliamps (one amp) for one hour, or 500 milliamps for two hours.
1,000 mAh = 1 amp flowing for 1 hourSo 5,000 mAh is five amp-hours of stored charge, whether it trickles out slowly or fast.
The "milli" just means thousandths. Phone and power bank makers use mAh because the numbers land in a friendly range, a few thousand, rather than decimals like 4.3 Ah. On a laptop or a camping battery you're more likely to see watt-hours, which we'll get to.
One thing mAh does not tell you is speed. A 20,000 mAh bank can charge your phone slowly or quickly; that's down to its output in watts. Capacity is the size of the tank. Watts are the width of the hose.
You'll see mAh on phone spec sheets, power bank boxes, earbud cases and smartwatches. Apple is the odd one out: it doesn't list mAh on its iPhone spec pages, so iPhone capacities come from regulatory labels, which is why they circulate as oddly precise figures like 3,692 mAh. Samsung and Google usually quote a "typical" capacity, a rounded figure slightly above the guaranteed minimum.
02How big is your phone's battery?
Current phones mostly sit between about 3,100 and 5,100 mAh. Thin phones are at the bottom of that range, and big Pro Max and Ultra models at the top. That's why a pocket bank that fully refills an iPhone Air leaves a Galaxy Ultra at around two-thirds.
| Phone | Battery | Smallest common bank for one full charge |
|---|---|---|
| iPhone Air | 3,149 mAh | 5,000 mAh |
| iPhone 17 | 3,692 mAh | 10,000 mAh (a 5,000 gets you most of the way) |
| iPhone 17 Pro | 4,252 mAh | 10,000 mAh |
| iPhone 17 Pro Max | 5,088 mAh | 10,000 mAh |
| Galaxy S26 | 4,300 mAh | 10,000 mAh |
| Galaxy S26 Ultra | 5,000 mAh | 10,000 mAh |
| Pixel 10 | 4,970 mAh | 10,000 mAh |
Want the exact number of refills for your phone and bank? The power bank calculator does it for cable and wireless charging.
03Why 10,000 mAh doesn't mean two full charges
Here's the part that trips people up. A 10,000 mAh bank and a 5,000 mAh phone look like a 2-to-1 match. In practice you'll get about 1.3 charges. Two things eat the difference.
- Voltage. The bank's mAh is counted at its lithium cells' voltage, about 3.6 to 3.7 V. USB sends power out at 5 V or higher, and the same energy at a higher voltage is fewer milliamp-hours. So the mAh on the box was never going to arrive one-for-one.
- Conversion losses. The bank boosts voltage up, the phone steps it back down, and each step turns some energy into heat. Cables and warm batteries take a little more.
Many banks print two numbers: the headline cell capacity (say 10,000 mAh at 3.7 V) and a smaller rated capacity at 5 V, often around 6,000 mAh. The rated figure is much closer to what your phone actually receives.
This is also why comparing mAh across very different devices goes wrong. A laptop battery runs at a higher voltage than a phone's, so the same mAh holds more energy. Watt-hours fix that by folding voltage in. Our mAh vs Wh guide shows the conversion.
04Reading a power bank label in 30 seconds
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Find the headline mAh
Usually the biggest number, like 10,000 mAh or 20,000 mAh. It's the cell capacity, the figure used for marketing.
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Find the rated capacity
Look for "rated capacity" with a voltage beside it, often 5 V. Use this one to estimate real phone charges.
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Find the Wh
Watt-hours are what airport security checks. Under 100 Wh is fine in your carry-on; see the flying rules for the rest.
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Check the output watts
"USB-C PD 20W" or higher means it can fast-charge a recent iPhone or Galaxy over a cable. A plain 5V/2A port (10W) will be slow.
If a label is missing the rated capacity and the Wh, treat that as a small warning sign. Reputable banks usually show both, because airlines ask for Wh.
05Is more mAh always better?
No. Extra capacity costs you in ways the number doesn't show:
- Weight. Capacity is mostly lithium cells, so a 20,000 mAh bank weighs close to double a 10,000 mAh one.
- Recharge time. A bigger bank takes proportionally longer to refill, and slow input can turn that into an overnight job.
- Flight limits. Past about 27,000 mAh at 3.7 V you cross 100 Wh, the carry-on comfort line.
- Unused capacity. If you only ever need half a charge on the commute home, you're carrying the rest for nothing.
Most people are best served by 10,000 mAh for daily carry and 20,000 mAh for travel. The 10,000 vs 20,000 mAh comparison walks through who needs which.
From a 5,000 mAh magnetic pocket bank to a 20,000 mAh travel brick.
Questions people ask
Is higher mAh better for a phone battery?
Generally, yes: more mAh means more stored charge and usually longer battery life. But screen, chip and software efficiency matter too, so a phone with a smaller battery can still outlast one with a bigger battery.
What does 5000 mAh mean?
It means the battery holds 5,000 milliamp-hours of charge, or 5 amp-hours. On a phone, that's a large battery. On a power bank, it's a pocket size that refills a smaller iPhone about once and a big Android to roughly two-thirds.
How many mAh do I need in a power bank?
Take your phone's battery size and divide by about 0.65 for one full charge. For most phones that lands near 6,000 to 8,000 mAh, so a 10,000 mAh bank is the practical pick for one full charge plus some spare.
Does mAh affect charging speed?
Not directly. Speed depends on watts: the bank's output, the cable, and what your phone accepts. A 10,000 mAh bank with 20W USB-C PD will charge an iPhone faster than a 20,000 mAh bank limited to 10W.
What's the difference between mAh and Wh?
mAh measures charge; Wh measures energy. Wh includes voltage, so it's fair across different devices. Multiply mAh by the voltage and divide by 1,000 to get Wh.