How to Test Capacity of Power Bank: Practical Guide for Canadians

Power banks have become a must-have for keeping devices charged on the go, especially for Canadians who spend time commuting, traveling, or exploring the outdoors. But if you’ve ever wondered why your power bank doesn’t seem to last as long as its label claims, you’re not alone. Figuring out the real capacity is something many users want to know before relying on their device for a full day.

In this guide, you’ll learn how to test the capacity of a power bank using practical, easy-to-follow steps. We’ll also cover why the advertised mAh can differ from what you get, and how to keep your power bank working at its best.

Why Advertised mAh isn’t Always What You Get

Many people assume that a 10,000mAh power bank should deliver exactly 10,000mAh of charge to their devices. But in real-world use, it often provides only 70%–90% of that. Why the difference? Let’s break it down.

The capacity listed on your power bank—such as 10,000mAh or 20,000mAh—is based on its internal battery cells. However, what your device receives is usually less because of voltage conversion and energy loss.

When a power bank charges your phone, it converts its stored energy from around 3.7V (cell voltage) to 5V or higher. During this conversion, about 10–30% of the energy is lost as heat. For example, a 10,000mAh power bank may provide only around 7,000mAh of usable power.

Some power banks, especially lower-cost models, tend to exaggerate their mAh ratings, advertising capacities that don’t reflect real-world performance. As a result, after accounting for energy lost during voltage conversion, the actual usable power can be even lower than expected. On top of that, temperature can further affect performance. In cold conditions, like Canadian winters, battery efficiency drops significantly, sometimes by 20% or more, making your power bank even less effective.

How to Measure the Capacity of a Power Bank

To find out how much energy your power bank really stores and delivers, you’ll need to run a test. Two simple tools—USB power meters and multimeters—can give you accurate readings.

Below are two step-by-step methods to test your power bank’s capacity effectively.

Test by Using a USB Power Meter: StepbyStep Instruction

A USB power meter is a small device that plugs between your power bank and your device to measure how much energy flows through. Here’s how you can use it:

1. Get a USB power meter.They are inexpensive and widely available online.
2. Fully charge your power bank.Start with 100% to ensure accurate results.
3. Connect the USB power meter.Plug it into the power bank’s output port.
4. Attach a load device.This can be your smartphone or a USB load tester that draws a consistent current.
5. Record the reading.The meter will show voltage, current, and the total mAh delivered.
6. Repeat the test.For the best accuracy, run the test until the power bank is completely drained.

Once you’ve recorded the mAh output from each test, simply calculate the average to get a more reliable estimate of your power bank’s actual usable capacity. For example, if your 20,000mAh power bank delivers 17,000mAh, that’s an 85% efficiency rate, which is typical due to energy loss during voltage conversion.

Test by Using a Multimeter: StepbyStep Instruction

A multimeter is a more technical tool but gives precise results when used correctly. You’ll need a bit of patience for this method to check capacity of power bank:

1. Prepare your multimeter.Set it to measure voltage and current.
2. Use a USB breakout board or connector.This helps you connect the multimeter between the power bank and your device.
3. Connect your power bank to a load.As with the USB meter, you can use your phone or a USB load tester.
4. Measure the current and voltage.Note the readings at regular intervals.
5. Calculate total energy output.Multiply current (A) by time (hours) and voltage (V) to find the watt-hours, then convert to mAh using the formula:
   mAh=(Wh÷5V)×1000mAh.

For example, if your readings show 18Wh of total energy, the calculation is:

(18 ÷ 5) × 1000 = 3,600mAh.

If the power bank is rated at 5,000mAh, this means you’re seeing about 72% efficiency, which is perfectly normal.

Factors Affecting Capacity Measurement Accuracy

Even with the best tools, several factors can skew the results of your test.

Cable Quality

Low-quality charging cables increase resistance, causing additional power loss. A thicker, well-insulated cable ensures more efficient energy transfer and a more accurate test result.

Load Variability

Smartphones and tablets don’t draw a constant current when charging. This fluctuation can slightly impact the final mAh reading, especially if you’re not using a stable USB load tester.

Temperature Effects

Cold weather, common in Canada, can make batteries less efficient. On the flip side, overheating during charging also affects overall performance and testing results.

Tips to Prolong the Battery Life of Your Power Bank

A few simple habits can help you maintain your power bank’s health for years:

• Avoid full discharges.Keeping the charge between 20% and 80% can reduce stress on the cells.
• Charge it every few months.If you don’t use it often, top it up to prevent deep discharge.
• Keep it cool.Store your power bank at room temperature. Heat and freezing conditions shorten battery life.
• Use proper chargers.Fast-charging adapters from reliable brands ensure steady and safe power input.

If you want a reliable power bank that maintains close-to-rated capacity, consider these trusted options:

Anker Power Bank (25K, 165W, Built-In and Retractable Cables)

The Anker Power Bank (25K, 165W, Built-In and Retractable Cables) is a solid pick for anyone juggling multiple devices. With three 100W USB-C ports, it easily powers a MacBook, phone, and tablet at the same time. The built-in cables—one extendable and one doubling as a strap—cut down on clutter and feel durable. Plus, its 25,000mAh capacity and carry-on-safe design make it a reliable companion for travel days or long commutes.

Anker Prime 27,650mAh Power Bank

The Anker Prime 27,650mAh Power Bank is compact but powerful, delivering up to 250W through two USB-C and one USB-A port. It can charge a MacBook Pro to 50% in under 30 minutes, and still have room to top off a phone or two. With fast 170W recharging and an app that shows real-time charge status—or helps locate it with a sound alert—it’s a smart choice for frequent flyers or heavy device users.

Conclusion

Knowing how to test capacity of power bank helps you understand what to expect and ensures you’re not caught off guard when you need power the most. With a USB power meter or multimeter, you can easily check the real mAh and keep an eye on its health. Pair these tests with good habits, and your power bank will serve you well for years.

Ready for a reliable power bank that keeps its promises? Check out Anker’s latest models designed for efficiency and durability.

FAQs

How do I check the capacity of my power bank?

To check capacity, use a USB power meter or multimeter while the power bank charges a device. Measure the total mAh delivered during a full discharge cycle, then compare this number to the advertised capacity. Keep in mind that an efficiency of 70–90% is normal because of voltage conversion and energy loss.

Is there a way to test a power bank?

Yes. The simplest way is with a USB power meter, which records voltage, current, and total energy output during charging. Another method involves using a multimeter and calculating watt-hours (Wh) converted to mAh. Both methods give you a realistic picture of your power bank’s actual performance and efficiency.

What is the actual capacity of a 20,000mAh power bank?

A 20,000mAh power bank usually delivers around 14,000–18,000mAh of usable power. This difference happens due to the conversion from 3.7V (cell level) to 5V or higher, plus small energy losses in the circuitry. High-quality models, like those from Anker, tend to stay closer to the higher end of this range.

Why is my 10,000mAh power bank only giving me 7,000mAh?

This happens because a portion of energy is lost during voltage conversion, which is normal. A typical power bank operates at 70–85% efficiency, meaning a 10,000mAh device often delivers around 7,000–8,500mAh. If your capacity is significantly below this range, it may be due to aging cells or low-quality components.