Power bank capacity is the mAh figure printed on the battery cell, and it is not the charge your phone receives. For most people, a 10,000mAh bank covers a phone once or twice, and a 20,000mAh bank suits travel or charging more than one device. The number that decides whether a bank can fly with you is the watt-hour (Wh) rating, which you work out from the label.
This is desk research: nothing here was tested, bought or used by this site, and the figures are what the makers and their guides state.
What mAh means, and why you get less than the label says
PITAKA’s buying guide explains that the number on a bank is usually battery capacity. Its example is a bank marked 10,000mAh at 3.8V, which stores 38Wh. When the bank charges a phone at 5.1V, the same energy gives a lower mAh figure, and some energy is lost in conversion. Its arithmetic gives about 7,450mAh at 5.1V before losses. It says most banks convert at 80–90%, so a 10,000mAh bank gives roughly 6,000–7,000mAh of rated output.
AOHi’s mAh guide is more conservative. It says a bank typically delivers only about 70–85% of its advertised mAh to your devices. The two guides give different loss figures, so size your bank with the lower number in mind.
How to check the voltage on a power bank
Read the printed label. PITAKA’s guide says the rated input shows the voltage the charging adapter must connect to, and the rated output has to match the output voltage of the adapter your phone uses. It also says it is not recommended to charge a phone with a bank that has different voltages. Some labels print the cell voltage next to the capacity, as in its 10,000mAh 3.8V example, while AOHi uses 3.6V for its single cell. Cell voltage differs by maker, so use the figure on your own unit when you do the Wh math.
How do you measure the capacity of a power bank?
You cannot read the true capacity from the label alone. Start with the label math: multiply the mAh by the cell voltage and divide by 1,000 to get watt-hours. AOHi states this as Wh = (mAh × V) ÷ 1,000. Then expect less than the printed mAh at your phone’s voltage, as described above. PITAKA says professional tools would give a rated-output result not too different from its calculation, and that cycle-life testing involves specific equipment, so for most buyers the practical check is the label math plus the maker’s stated figures.
How much power should a portable power bank have?
AOHi’s guide sorts banks into three tiers: 5,000–10,000mAh for everyday use, 15,000–20,000mAh for travel or work, and 30,000–40,000mAh for heavy users. PITAKA’s guide cites capacities from 500mAh to 30,000mAh, and AOHi sells a 40,000mAh model. For a bank you carry on a plane, the Wh limit is the practical ceiling. AOHi’s device table shows how far a 10,000mAh bank goes:
| Device | Typical battery (per AOHi) | Full charges from 10,000mAh (per AOHi) |
|---|---|---|
| Smartphone (iPhone / Android) | ~3,000–5,000mAh | 1.5–2x |
| iPad / Tablet | ~7,000–10,000mAh | ~1x |
| Switch / Steam Deck | ~4,300–6,500mAh | ~1.5x |
PITAKA’s own calculation uses rated capacity and an iPhone 11 battery of 3,110mAh, and gets about 2.25 charges from a 10,000mAh bank. The two guides use different methods, so compare the method, not only the number.
10,000mAh or 20,000mAh: which should you get?
If you charge one phone about once a day and want something light, 10,000mAh is usually enough. If you travel, work away from outlets, or charge a phone and a tablet together, AOHi’s travel tier of 15,000–20,000mAh is the better fit. PITAKA’s guide flags the trade-off: higher capacity means a bigger unit. If you are comparing one wireless model, see our lit solar wireless powerbank review. If a bank cannot cover what you need, such as running a small appliance, our page on is it worth buying a portable power station covers the price, runtime and limits.
How long will a power bank last?
PITAKA’s guide says most banks are rated at 300 to 1,000 charge cycles, and it advises avoiding any bank with fewer than 500. Its formula is lifespan = cycles × charging rate ÷ daily use. For a 10,000mAh bank with a charging rate of 2.25, 500 cycles and one full charge a day, it works out to 1,125 days, about 3.08 years. PITAKA says the number of phone charges is usually not written on the bank, and that for cycle life you should ask the seller before you purchase.
Can you bring a 30,000mAh power bank on a plane?
AOHi’s guide says most airlines allow power banks under 100Wh in carry-on luggage, and that a bank over 100Wh may still be allowed with airline approval. A 30,000mAh bank is over that line, so check your airline’s rules before you fly. AOHi’s formula puts a 30,000mAh bank at 108Wh at its 3.6V cell voltage. At 3.8V, the cell voltage in PITAKA’s example, the same formula gives 114Wh (our calculation). Either figure is over the 100Wh line.
| Capacity | Wh at 3.6V | Wh at 3.8V |
|---|---|---|
| 10,000mAh | 36 | 38 |
| 20,000mAh | 72 | 76 |
| 27,600mAh | 99.36 | 104.88 |
| 30,000mAh | 108 | 114 |
| 40,000mAh | 144 | 152 |
AOHi says a bank over 100Wh may still be allowed with airline approval. Its advice is to contact the airline in advance and send the MSDS (Material Safety Data Sheet). Our power station labels guide explains watt-hour figures further.
How strict is TSA with power banks, and what is the largest approved size?
The 100Wh figure in AOHi’s guide is the common carry-on line to check against. For screening rules and the largest size your airline will accept, check the TSA’s website and your airline’s current baggage rules before you pack.
How fast does a power bank charge, and what does the adapter change?
PITAKA’s guide says charging time equals battery capacity divided by the actual input current, and that the input current equals the output current of the charger. Its example: a 10,000mAh bank on a 5V/1A adapter takes about 10 hours, and on a 5V/2A adapter about 5 hours. Your adapter sets the pace, so check its rating as well as the bank’s.
Is a holiday power bank deal worth it?
Before you buy at a holiday price, check these five things:
- Capacity: work out the Wh from the label so the bank works on your flight.
- Real output: size the bank with the 70–85% or 80–90% range from the two guides, not the printed mAh.
- Total cost: add the adapter and cable you need, since charging speed depends on the adapter.
- Returns and warranty: AOHi’s blog lists free worldwide shipping on orders of $49.99 or more and an 18-month warranty, as of October 21, 2026. Read the return window and warranty terms at checkout before you pay.
- Price: prices and bundles change, so check today’s price directly with the seller.
Safety and recall checks
PITAKA’s guide says to look for damage to the case, corrosion on the connectors and markings you can read. It says the protection functions (over-current, under-voltage, short-circuit, over-temperature and overvoltage) can usually be found in the user manual. It also says CE, RoHS and FCC marks are common on electronics, and that FCC is mandatory for the US market. Before you buy, check the maker’s site for recall notices on your exact model number.
Before you order
- Write down the printed mAh, cell voltage and Wh figure.
- Check your airline’s carry-on rules if you will fly.
- Ask the seller for the cycle rating and manufacture date.
- Add the adapter and cable to the total cost.
- Confirm the return window and warranty before you pay.
By InfinitePowerSolutions.com Technology Desk
