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01Pick by how you'll use it
Choosing between a 10000 and 20000mAh power bank comes down to how long you go without an outlet. If you're home most nights, 10,000 mAh covers a full phone charge with spare. If you're away for days or charging two devices, 20,000 mAh earns its extra weight.
10,000 mAh
- About 37 Wh
- 1.3 to 2 full phone charges over a cable
- Fits a jacket pocket
- Refills from the wall in a few hours
20,000 mAh
- About 74 Wh
- 2.5 to 4 full phone charges
- Can top up a tablet or a second phone
- Close to double the weight
A useful test: think about the last month. If your phone died before you got home once or twice, the smaller bank solves it. If you regularly spend whole days away from outlets, or you're the person friends ask for a charge, the larger bank pays for its weight. Buying the 20,000 "just in case" often means it stays in a drawer because it's too heavy to bother with.
0210,000 vs 20,000 mAh by the numbers
| 10,000 mAh | 20,000 mAh | |
|---|---|---|
| Energy (at 3.7 V) | About 37 Wh | About 74 Wh |
| iPhone 17 (3,692 mAh) | About 1.8 charges | About 3.6 charges |
| iPhone 17 Pro Max (5,088 mAh) | About 1.3 charges | About 2.6 charges |
| Galaxy S26 Ultra (5,000 mAh) | About 1.3 charges | About 2.6 charges |
| Refill time with 20W input | Roughly 2.5 to 3 hours | Roughly 5 to 6 hours |
| Refill time with 10W input | Roughly 4 to 5 hours | Roughly 9 to 10 hours |
| Weight | Around a phone's weight | Close to double |
| Carry-on OK? | Yes | Yes |
The refill time is the cost people forget. A big bank with a slow input can take all night to fill, so if you pick 20,000 mAh, look for USB-C PD input and pair it with a 20W or faster wall charger. Our wall charger guide covers what to plug it into.
Size follows capacity too. Lithium cells make up most of a power bank's bulk, so there's no trick that makes a 20,000 mAh bank as small as a 10,000 mAh one. Slim 20,000 mAh banks exist, but they get slim by getting longer and wider, which still rules out most pockets.
What about two 10,000 mAh banks instead?
+Why two can beat one
- Carry one on light days, both on long ones
- Charge two phones at full speed at the same time
- Two people can each hold one
- If one fails or gets left behind, you still have a backup
–The catch
- Two things to remember to recharge
- Uses both of your two-bank airline allowance
- Usually costs more than one 20,000 mAh bank
- Two sets of cables and ports to manage
03Try it with your phone
Charging wirelessly knocks roughly a quarter off these figures. If you're weighing a magnetic pack against a cable bank too, see magnetic vs regular power banks.
04Three ordinary days, sized up
Office day with a long commute
You leave at 7 a.m. and get home at 7 p.m., with a dead phone by mid-afternoon. You need maybe half a charge. 10,000 mAh covers that twice over; 20,000 mAh is dead weight in your bag every day.
Long-haul travel day
Airport, flight, connections, maps on arrival, plus earbuds. Under the 2026 rules you can't recharge a bank on board, so you need to start with enough. 20,000 mAh is the safer pick. The details are in power bank rules for flying.
Weekend camping for two
Two phones, two nights, photos and offline maps. That's roughly three or four full charges between you. 20,000 mAh, or two 10,000 mAh banks so you each carry one. For longer trips, see whether a solar bank is worth adding.
05When neither size is right
- 5,000 mAh if you only ever need an emergency top-up. It's about one full charge for an iPhone Air and two-thirds for larger phones, and small magnetic versions snap on.
- 26,800 mAh if you want the most capacity that still flies. It lands just under 100 Wh.
- 30,000 mAh and up only for laptops or off-grid use. At 3.7 V it's about 111 Wh, over the carry-on comfort line, so it's a poor travel pick.
Whichever size you choose, look for USB-C PD output of at least 20W. A 10,000 mAh bank with fast output will get you out the door sooner than a 20,000 mAh one stuck at 10W. The units are explained in mAh vs Wh.
Compact 10,000 mAh banks for every day and 20,000 mAh banks for longer trips. All under 100 Wh.
Questions people ask
Is 10000mAh enough for a day?
For most people, yes. It's about one and a half to two full charges for a typical phone, which covers a heavy day with room to spare. If you're away from outlets for several days, step up to 20,000 mAh.
How many times will a 20000mAh power bank charge a phone?
About 2.5 to 4 times over a cable, depending on battery size. An iPhone 17 gets around 3.6 charges; a Pro Max or Galaxy Ultra gets around 2.6. Wireless charging lowers that by roughly a quarter.
Can I take a 20000mAh power bank on a plane?
Yes, in your carry-on. At 3.7 V it's about 74 Wh, comfortably under the 100 Wh limit. Never put it in checked luggage.
Is a 20000mAh power bank too heavy to carry?
It's fine in a backpack or tote but awkward in a pocket, at close to double the weight of a 10,000 mAh bank. If you'd leave it at home because of the weight, the smaller bank is the better buy.
Does a bigger power bank charge my phone faster?
No. Speed depends on the bank's output wattage and your cable, not its capacity. A 10,000 mAh bank with 20W USB-C PD charges as fast as a 20,000 mAh bank with the same output.