Power bank buying guide: capacity, watts and flying rules in Canada

A good power bank can rescue a long travel day, a camping weekend or a cold afternoon on the ski hill when your phone battery drops faster than expected. But the numbers on the box, mAh, Wh and watts, don’t always tell the story you’d expect. This power bank buying guide explains what those figures mean, how many charges you’ll really get and what Canadian flying rules allow in your carry-on.

Power bank buying guide basics: mAh vs Wh

Capacity is usually shown in milliamp-hours (mAh). That figure describes the charge stored at the voltage of the battery cells inside, not at the voltage your phone charges at. Watt-hours (Wh) measure the energy stored. They’re the more useful number for comparing batteries, and they’re the number airlines care about.

To convert, multiply mAh by the cell voltage and divide by 1,000:

Wh = mAh × V ÷ 1,000

Most power banks use lithium cells with a nominal voltage of around 3.6 to 3.7 V. That means a 10,000 mAh power bank typically stores about 36 to 37 Wh, and a 20,000 mAh model about 72 to 74 Wh. The exact Wh rating is usually printed on the power bank’s label, so check it rather than relying on an estimate.

Watts: how fast a power bank charges

Watts (W) measure power, or how quickly energy moves. A power bank’s output rating tells you the maximum it can deliver to a device. More watts generally means faster charging, but only up to what your phone, the power bank and the cable can all handle together.

• A phone charges at the lowest common speed supported by the phone, the power bank and the cable.
• Fast-charging standards vary between brands, so a phone may charge more slowly on a power bank than on its own wall charger.
• If a power bank has more than one port, its total output is usually shared when you charge several devices at once.
• Check the input rating too, since it determines how quickly the power bank itself recharges.

For example, a phone that supports 100 W wired charging can draw at most 22.5 W from a 22.5 W power bank. That’s still useful for topping up on the go; you’ll just get the fastest speeds from a compatible wall charger.

How many charges will you really get?

You’ll never get the full rated capacity into your phone. Energy is lost converting the cells’ voltage up to the charging voltage, as heat, in the cable and in the phone’s own charging circuit. As a rough rule of thumb, expect about 60 to 70% of a power bank’s rated mAh to end up in your phone’s battery.

Phone battery	10,000 mAh power bank	20,000 mAh power bank
5,000 mAh (a common size for many phones)	About 1.2 to 1.4 charges	About 2.4 to 2.8 charges
7,700 mAh (a large phone battery)	About 0.8 to 0.9 of a charge	About 1.6 to 1.8 charges
10,000 mAh (a very large phone battery)	About 0.6 to 0.7 of a charge	About 1.2 to 1.4 charges

These are estimates, not test results. Real numbers depend on the phone, the cable, the temperature and whether you use the phone while it charges. Cold matters in Canada: lithium batteries deliver less energy when they’re cold, so keep your power bank in an inside pocket on winter days.

Flying with a power bank in Canada

Power banks count as spare lithium batteries, so specific rules apply when you fly. These are the key points for flights in Canada:

• Carry-on only. Power banks are not allowed in checked baggage. If your cabin bag gets gate-checked, take the power bank out first.
• Under 100 Wh: allowed in your carry-on.
• 100 to 160 Wh: allowed only with airline approval.
• Over 160 Wh: not allowed.

A 10,000 mAh or 20,000 mAh power bank typically falls well under 100 Wh, but always confirm the Wh figure printed on your specific model. If the label only shows mAh, use the formula above with the cell voltage shown on the label.

Tips for the airport

• Keep the power bank where you can reach it, and protect the ports from short circuits, for example in a pouch or case.
• Make sure the label is readable, since security staff may want to check the rating.
• Airlines can set stricter rules than the baseline, such as limiting how many spare batteries you carry or whether you can use a power bank during the flight.
• Rules can change, so check with your airline and Transport Canada before you fly, including every airline on connecting or international trips.

Which power bank capacity should you choose?

For everyday carry: around 10,000 mAh

A 10,000 mAh power bank typically stores about 36 to 37 Wh, which works out to a little over one full charge for a common 5,000 mAh phone battery, based on the estimates above. It’s a sensible size for commuters and students who want a meaningful top-up during the day. Check that your phone can make use of its output.

For trips and long weekends: around 20,000 mAh

A 20,000 mAh model, at about 72 to 74 Wh, doubles the capacity and gives roughly 2.4 to 2.8 charges for a 5,000 mAh phone. It suits camping, road trips and travel days, especially if you have a big-battery phone or more than one device to charge. Expect a heavier, bulkier unit; it still typically falls well under 100 Wh, the level above which you need airline approval.

Shopping now? Our accessories section carries three power banks: a 10,000 mAh ultra-slim magnetic power bank with 20 W output and an LED percentage display, a magnetic wireless power bank with a fold-out kickstand rated for 15 W wireless charging, and a mini pocket power bank with a built-in connector and phone stand for quick top-ups. Each listing says what its product sheet confirms, including where a capacity isn’t stated.

Quick checklist before you buy

1. Match capacity to how many charges you need, allowing for 30 to 40% conversion losses.
2. Check the output in watts and whether your phone can make use of it.
3. Find the Wh rating if you plan to fly.
4. Pack it in your carry-on, never in checked bags.

Find more practical advice on our blog, such as our guide to choosing the right TV size.