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, the REDMI Note 17 Pro Max 5G supports 100 W HyperCharge wired charging, but on a 22.5 W power bank it can draw at most 22.5 W. 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 (REDMI Note 17 and Note 17 5G)	About 0.8 to 0.9 of a charge	About 1.6 to 1.8 charges
8,340 mAh (REDMI Note 17 Pro 5G)	About 0.7 to 0.8 of a charge	About 1.4 to 1.7 charges
10,000 mAh (REDMI Note 17 Pro Max 5G)	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 should you choose?

For everyday carry: Xiaomi Power Bank 10000mAh 22.5W Lite

The Xiaomi Power Bank 10000mAh 22.5W Lite offers 10,000 mAh of capacity and 22.5 W output in a white Lite model, for $24.99 CAD. It’s a sensible pick for commuters and students who want a meaningful top-up during the day.

For trips and long weekends: REDMI 20000mAh 18W Fast Charge Power Bank

The REDMI 20000mAh 18W Fast Charge Power Bank doubles the capacity to 20,000 mAh with 18 W fast charging, for $34.99 CAD. It suits camping, road trips and travel days, especially if you own a big-battery phone such as the REDMI Note 17 5G.

Both power banks cost less than $99 on their own, so standard shipping of $14.99 applies unless your order goes over $99; adding one to a phone order gets you free shipping. Browse all accessories and phones, and see our shipping policy for delivery times.

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.