What Size Power Bank Do You Need for a 3-Day Trip?

On a 3-day trip at 60% efficiency, if you can charge at the hotel each night, a phone alone just barely gets by on 10,000mAh. A tablet or handheld console needs 20,000mAh, and a laptop 25,000mAh. With no outlet for 3 days and a phone alone, carry 20,000mAh and 10,000mAh banks.

Power bank size for a 3-day trip at a glance

Assuming 1 charge a day (half for tablets and laptops) at 60% efficiency, the size you need comes out like this.

5,000mAh may not fill even the iPhone 18 Pro, the smallest battery here, from 0% to 100% once. Use it as a half-day spare, not as your main bank for 3 days.

Why a power bank charges less than its label says

The label shows the battery inside the bank, and some power is lost while charging. Wh (watt-hours) is capacity times voltage, so it compares different devices. Conversion efficiency is the share you can actually use.

A 10,000mAh power bank holds 37Wh, and about 22-26Wh (60-70%) reaches your device. Power is lost as heat when it is drawn out over USB and again when the device battery charges. The makers’ figure of about 6,000-7,000mAh counts at USB’s 5V (30-35Wh), while this article assumes more loss.

10,000mAh charges an iPhone 18 Pro about 1.3 to 1.8 times. Dividing 10,000mAh by its 4,056mAh battery gives 2.5, but power is lost along the way, so the real number is lower. The 4,056mAh is an EU-label figure from press reports; Apple does not publish it.

Per the makers’ figures as of October 2026, wireless charging is less efficient than a cable, so expect fewer charges than the wired figures here..

Charging at the hotel, and not charging

If you can charge each night and carry only a phone, 10,000mAh just barely covers a day. The margin is only about 0.8Wh. The Pro Max’s 5,391mAh is an EU-label figure from press reports (Apple does not publish it), and the US models are unchecked, so 20,000mAh is safer for a Pro Max.

With no outlet for 3 days, a phone alone needs 20,000mAh and 10,000mAh banks. A tablet or console raises the need.

An iPad Air 11-inch with a Pro Max needs about 105.7Wh; two 25,000mAh banks (about 108Wh) cover it. With a Switch 2, an iPhone 18 Pro needs about 107.2Wh and just barely fits, but a Pro Max needs about 122.6Wh and does not. A Steam Deck or MacBook Air does not fit, so charge fewer times or recharge on the way.

Per Amtrak’s website, every seat in Amtrak unreserved coach has a 120V outlet, so charging on board lets you carry less. It varies by train and service.

How to check your own devices

1. Find each device’s battery capacity. If it’s listed in Wh, use that. If it’s only in mAh, convert it to Wh in the next step. The table below shows which unit is published.
2. Multiply mAh × voltage ÷ 1000 to get Wh. The voltage wasn’t found in the official specs, so use 3.85 V to avoid underestimating.
3. Multiply by your charges from the bank: one day’s worth if you can charge each night, all the days if you can’t. A phone is 1 charge a day.
4. Multiply the power bank’s Wh by the conversion efficiency from the section above to get what you can actually use. Compare that with your total.

To share one bank, add each person’s Wh and pick a size from the table. This assumes you can charge each night and each person charges a phone once a day. If both carry only a phone, two of the largest phone here need about 41.6Wh, so 20,000mAh (at least 43.2Wh usable) is the guide.

With a camera, add its battery Wh: Sony’s NP-FZ100 is 16.4Wh, and the GoPro Enduro is about 7.3Wh at an assumed 3.85V. A phone of about 20.8Wh plus the NP-FZ100 comes to about 37.2Wh, or 28.1Wh with the GoPro. Both fit within 20,000mAh if you charge one camera battery a day; a battery listed only in mAh needs its voltage to get Wh.

Apple Watch and AirPods don’t publish their Wh, so they aren’t counted.

In the calculator, pick your devices, whether you can charge each night and the number of days. It shows the Wh you need and which of 5,000, 10,000, 20,000 and 25,000mAh is enough. If one bank isn’t enough, it shows a two-bank combination.

Taking a power bank on a plane

Under FAA rules, power banks of 100Wh or less can be carried on without airline approval. Those of 101 to 160Wh need the airline’s approval, and none can go in checked baggage. 25,000mAh is about 96Wh even at 3.85V, inside the 100Wh limit.

Some airlines, such as Southwest, allow only 1 power bank per person, so check your airline’s rules.

Under Japan’s rules since April 24, 2026, if you fly a Japanese airline, you may carry up to 2 power banks of 160Wh or less in the cabin. None can go in checked baggage. You may not charge a bank, or charge a device from a bank, on board.

With no outlet for 3 days, two banks fit Japanese airlines’ limit of 2. An airline that allows only 1 won’t let you carry both.

Beyond the FAA, Southwest and Japanese airlines, other rules aren’t covered here.

Picks for each situation

Candidates have 100 or more ratings, 4.0 or more stars, a seller that is Amazon or the maker, and no parallel imports.

Of the products checked here, these are the cheapest that meet the conditions (as of October 2026). If you carry only a phone and can’t charge for 3 days, combine a 20,000mAh pick with a 10,000mAh pick.

Phone only, and you can charge at the hotel each night

10,000mAh just barely covers a day of phone charging alone, with about 0.8Wh to spare.

A tablet or handheld console besides your phone, and you can charge at the hotel each night

20,000mAh with two or more output ports, so it charges two devices at once.

A laptop too, and you can charge at the hotel each night

25,000mAh with a maximum output of 65 W or more, so it can charge a laptop too.

Sold by AnkerDirect, the maker's official store.

FAQ

Is 10,000mAh enough for a 3-day trip?

Assuming 60-70% efficiency and a 0% to 100% charge, if you can charge each night and carry only a phone, 10,000mAh just barely covers a day. The margin is only about 0.8Wh.

The Pro Max’s 5,391mAh is an EU-label figure from press reports (Apple does not publish it), and the US models are unchecked, so 20,000mAh is safer for a Pro Max.

Do I need 20,000mAh for a 3-day trip?

Assuming 1 charge a day (half for tablets and laptops) at 60% efficiency, with an outlet each night, 20,000mAh covers a phone plus a tablet or console. A phone plus a laptop needs 25,000mAh.

What size power bank do you need if you can’t charge for 3 days?

Assuming 1 charge a day (half for tablets and laptops) at 60% efficiency, with no outlet for 3 days, a phone alone needs 20,000mAh and 10,000mAh banks. A tablet or console raises the need.

How many times can a 10,000mAh power bank charge my phone?

Assuming 60-70% efficiency and a 0% to 100% charge, 10,000mAh charges an iPhone 18 Pro about 1.3 to 1.8 times. Dividing 10,000mAh by its 4,056mAh battery gives 2.5, but power is lost along the way, so the real number is lower.

The 4,056mAh is an EU-label figure from press reports; Apple does not publish it.

What size power bank should two people share?

To share one bank, add each person’s Wh and pick a size from the table. This assumes you can charge each night and each person charges a phone once a day.

If both carry only a phone, two of the largest phone here need about 41.6Wh, so 20,000mAh (at least 43.2Wh usable) is the guide.

Can I bring a power bank on a plane?

Under FAA rules as of October 2026, power banks of 100Wh or less can be carried on without airline approval. Those of 101 to 160Wh need the airline’s approval, and none can go in checked baggage.

25,000mAh is about 96Wh even at 3.85V, inside the 100Wh limit. Some airlines, such as Southwest, allow only 1 power bank per person, so check your airline’s rules.

Under Japan’s rules since April 24, 2026, if you fly a Japanese airline, you may carry up to 2 power banks of 160Wh or less in the cabin. None can go in checked baggage.

You may not charge a bank, or charge a device from a bank, on board.