Power Bank Ratings – mAh Explained
Power banks have now become a necessity for when you need to charge your phone and can’t find an outlet. However, a lot of users also find out that their own external battery pack does not provide as many full charge cycles as claimed. What we aim to do in this article is explain the science behind those capacity ratings, show why power banks do not always perform as claimed, and offer advice on how to measure real-world output. In the end, you will be able to identify a good brand and read true data so that you do not fall into the ubiquitous pitfalls of marketing from your mobile power station market.
It is standard for manufacturers to badge portable chargers with a capacity figure, typically expressed in milliamp-hours or mAH. That figure is the sum of all the charges the internal lithium-ion cells could hold (at their nominal voltage, usually 3.7 volts). Even using a 10,000 mAh power bank implies that it has 37 watt-hours of actual energy stored. But that stored energy still needs to be converted into useful output at the same voltage as a USB standard (5 volts), and there’s efficiency lost in heat during such voltage conversion.
The advertised output says one thing (whatever number of mAh is written on your battery/charger), the actual production that reaches a phone or tablet is another, lower thing because capacity ratings are reflecting the internal cell at 3.7V rather than the output voltage that charges up your device, which uses things at 5V. So in theory, 37 watt-hours divided by 5 volts gives you about 7,400 mAh of USB output—under ideal conditions. The voltage conversion circuitry is only about 85–90% efficient to start, and performance suffers due to ambient conditions as well. In practice, that 10,000 mAh power bank ends up being in the neighborhood of 6,500 mAh of usable charge.
Power bank is a semantically different keyword variation of external battery pack, backup battery, portable charging station. Still, not all products are as they may seem. Road warriors should read the fine print, though: Knowing the math of mAh to watt-hours and the voltage conversion losses can help you make more informed purchases right, at least until midday.
The Math of Capacity: Peak vs. Deliverable Throughput
Many established consumers also think that if a power bank has 10,000mAh, then there are at least two full phone charges in the bank. The reality is, every watt of stored energy has to pass through a boost converter that steps the voltage up to 5 V for USB—and at multiple stages, some loss occurs: charging the cells, stepping up to the target output, and discharging into your device.
Voltage Conversion Loss
Switching regulators step up voltage, but require significant power overhead in the way of heat. A converter that attains 90 percent efficiency, for example, lets ten percent of the energy slip away as heat. On a 10,000 mAh power bank (37 Wh), that equates to an approximate loss of 3.7 Wh wasted. In this case, you’re only getting about 3.7 Wh off the top before you even start charging anything, which eats into that advertised capacity rather severely.
Worse yet, many budget power banks use cheaper boost chips that are less efficient still, closer to 75 percent in real-world conditions. If you shop for these products, buyers should look for efficiency ratings or for chips are come from a reputable manufacturer. Indeed, these details are often found only in technical specifications and are buried deep down on a product’s page.
Efficiency and Temperature Effects
The single most important factor governing the performance of a lithium-ion battery is temperature. Cold crimps capacity, and heat breaks down cells faster than a Las Vegas marriage. An overnight in a freezing car may knock 20 percent or much more off the effective capacity of your power bank. On the other hand, charging and discharging well above 40 °C thermal cycle cells should only sacrifice their quoted useful life theoretically we presume some number of degrees Celsius before instant damage occurs… and if you live in a region where your power bank lives on top of the heater vent or it is particularly hot outside, then they may never reach expected end of lifecycle for this particular reason.
Manufacturers generally test capacity in a controlled environment: new cells at an ambient temperature of around 25 °C and with consistent discharge rates. Fluctuating currents while charging your phone (all power banks work by tricking your phone into thinking it’s plugged into the wall), temperature fluctuation, and cell aging can all decrease usable capacity by even more, which is why you never seem to get as much use out of your power bank as you think you should have.
Why Manufacturers Inflate Capacity Claims
Overstating capacity is not a coincidence. However, consumer perception is driven by marketing specifications, and 200 mAh always looks better than 150 or, god forbid, 50 mAh on the spec comparison chart. As a content strategist with more than 10 years of experience advising tech vendors, I have seen many product pages written to drive eyeballs rather than conversions.
Marketing Practices
Labels they would read from the front, like “20,000 mAh Ultra-Slim Power Bank” excite consumers but more often than not refer to a combination of capacities in cells measured at 3.7 V and listing that figure without noting expected conversion losses avoids regulatory concerns in regions where there is still little enforcement on how many mAh you can print on a package! Worse, some sellers wire numerous cells in parallel &/or compound their mAh ratings in series and take no account of inefficiencies.
Deceptive charging also often bypasses that information on the poorly crafted box about how many of those all-important charge cycles the device will endure before less than 80% of its original capacity is returned to it in actuality. On day one, this is a solid 20,000 mAh power bank, but it may drop to an actual performance of 15,000 mAh after only 300 charge and discharge cycles. It is very rare for buyers to think about performance in the long term on their initial purchases.
Testing Under Ideal Conditions
They’re typically rated at a small fraction of that—say, 0.5 amps—for test purposes because batteries do best with an easy discharge rate (more detail below). However, most smartphones use between 1-2A of charging when they need to charge in. This again causes a shift of the efficiency curves and, therefore, higher currents lead to higher losses. So while a power bank may test at 0.5 amps and perform with 90 percent efficiency, the same unit may only perform at 80 percent under a 2 amp load. Given the absence of any standardized way of testing these batteries industry-wide, it is very much an apples-to-oranges comparison.
How to Find Out the Actual Capacity of Your Power Bank
You can find affordable ways to check the real output if you suspect that your power bank delivers more than its trade value. A good USB power meter (a small inline device that measures voltage, current, and cumulative watt-hours) can show you how many mAh your battery bank truly outputs per charge to your device.
DIY Measurement Methods
And for those of you without a power meter, you can still get an idea of the capacity by charging your phone to 100 percent, and then hooking it up to the power bank until the charger automatically shuts off. Note the battery percentage used. On the other hand, with a power bank you may not be able to stretch it past 90 percent of the rated capacity; for example if your phone has a 3,000 mAh internal battery and you go from fully depleted to near empty on a single charge that’s about 2,700 mAh delivered (accounting for converting at similar low voltage) until your powerbank is also depleted. The results are not 100% perfect, but they do show how big the differences are between promised and real output.
Set your phone’s battery to drop to 20 percent before loading the tool for a fairer base comparison. Be sure to make them with the phone screen off and no wireless radios on to have the least possible parasitic drain. Do this a bunch of times, and you end up with a rough estimate for average usable capacity.
Capacity Measurement Tools and Apps
When it comes to peripherals, you can test current and voltage output in real-time with dedicated USB testers such as the Drok DC Digital USB Meter or the PortaPow Power Monitor, which also accumulates charge. At under twenty bucks a pop, they could save you 100s by keeping you from wasting your money on overhyped models. The more advanced testers provide you with the data log for a companion mobile app, providing efficiency curves and high-current performance assessment (check for throttling), even comparisons between different brands or discharge rates.
How to Select a Good Power Bank
If you shop around for an external charger, read the fine print closely. There Are Good Power Banks and Bad Power Banks. Part safety certifications, cell brand, smart charging further set apart reliable portables from beercan-tier (*see below) import names.
Certification and Standards
Check the shell for UL, CE, and FCC tags. These third-party safety certifications ensure that the power bank has at least some level of safe build quality and performance. The highest quality of all specific components in the Wagons overall is certified by USB-IF for Power Delivery (PD) and Quick Charge (QC) compliance, so you can be sure that the voltage conversion hardware is top-tier and proficient. We pay more for products with these logos because, by and large, they work as advertised.
Some manufacturers will name cell brands—Panasonic, Samsung or LG, etc. Name-brand cells typically have consistent performance and longer lives, so many high-quality power banks use them. Stay away from generic high-capacity cells that don’t have a name brand like “high-performance,” as they use lower-grade materials and run down immediately.
Brand Reputation and User Reviews
Given the ability of early peer reviews and forums to pick up on dubious patterns (misleading capacity claims, etc), we thought it might be worth taking a look at the drive for ourselves, to see how performance stacked up. Internet resources provide teardown reports and show the capacity of true cell, circuit, and build quality, as similarly done in r/powerbanks or specialized tech blogs. Brands that do not are usually brands that never deliver on claims of rating have nothing to hide with a clear spec sheet and third-party test results. When in doubt, consider companies that offer reliable warranties and an excellent customer service guarantee.
My Own Story Real Capacity Revealed
When I began testing different mobile charging solutions back in 2015, the first power bank I bought was claimed to be a 20,000mAh power bank from a large well well-known digital marketplace. It was finally able to power up my smartphone after three full cycles. With a USB meter in one hand and some spare dimes for playing Pac-Man in the device, I found it delivered more like 11,000 mAh. Sadly, that was not the case, so I dug into the casing only to find out that he used 4 pcs 5,000 mAh cells rated at 3.7 V with an inefficient boost converter. It taught me a lesson about valuing transparency and certification over marketing hype.
Over the past year, I’ve tested more than 50 models ranging from pocket-sized ultra-compact units to experimental new rugged designs designed for outdoor use. Without fail, as long as they stated true watt-hour figures, openly discussed their cell suppliers and had USB-IF approval, the batteries stayed within 10 percent of their rated capacity. Word of advice: do NOT be deceived by the shiny cover. Doing a bit of research upfront could not only save some huffing and puffing frustration, but also ensure you have power where you work best in the first place.
Conclusion
While power banks are a necessary evil required to get through modern life, the inflated capacity claims and variable efficiency tend to materialize in practice as you being left with 15% battery halfway through your day. Knowing this can help you buy batteries with realistic mAh ratings and prevent big losses from voltage conversion, and by testing their real output using very simple tools. Focus most of your attention on certified models that list accurate watt-hour capacities, name-brand cells, and fast charging. Now armed with this new knowledge, your next external battery will provide you with the unbeatable backup power that you have been patiently waiting for: no surprises or letdowns.
Frequently Asked Questions
Why does my power bank give a lower output than written?
Manufacturers love to measure performance at the internal cell voltage (3.7 V), while output is always delivered at 5 V through USB after many extra waste of energy are taken to bring down that input voltage. Padding”,_PADDING The through-efficiency lands between 80- and 90-percent depending on temperature and discharge rate, so that accounts for part of the lower output in the real world.
How do I measure the actual capacity of my in-home power bank?
The most accurate measurement was performed with a USB power meter, which logs voltage, current and accumulated watt-hours. Or in its absence, fill your phone, discharge the battery bank until it doesn’t start another charge cycle (assuming a universal figure of 1A at 5V = 5000mAh), and take the % drop multiplied by your known phone battery capacity.
Is Listing the Watt-Hour Ratings Compulsory for All Power Banks?
Regulations vary by region. Manufacturers opt for the mAh standard at 3.7 V, as it gives an inflated capacity perspective.eval(()=>{}) A watt-hour rating will provide you with a better idea of how much energy is stored, but it’s not as common except in the highest-end models. Look for these two specifications in power banks to ensure more transparency through the product details.
Does the power bank capacity reduce over time?
Yes. Each charge cycle degrades a lithium-ion cell, losing ten percent capacity after 300 to 500 cycles. This loss is only accelerated by high temperatures, deep discharges and fast charging. Batteries have a lifespan that can be stretched by storing correctly and charging at reasonable rates.
Is the charge rate linked to how much capacity is being delivered from a pack?
When a higher output current is drawn, the efficiency of the converter may decrease. Charge at 0.5 amps and you are reasonably close to the USB socket on a power bank’s rated capacity, but charge at two amps or more, and these voltage conversion losses increase very significantly. For anything where you prioritize total usable volume, look at things with smart current distribution or more output ports for staggered charging.
