A few weeks back I took my son on a school tour. We planned to stay at a hotel for two nights, but I wanted to pack light. I had just done a review on a small power bank that seemed perfect to use as my phone’s temporary charging system. I had tested all of its many features and they seemed to work well. The unit was small, and claimed an impressive 20,000 mAh of power. I felt that this should be enough to fully recharge my phone from zero more than four times.
My phone was at a 50% charge when I plugged it into the fully charged power bank. The next morning my phone was only at 84% charge, and the power bank was at 21%. Clearly, it did not have a 20,000 mAh battery. In fact, it likely didn’t even have a 5000 mAh battery. Yet, the print on its case clearly stated 20,000 mAh. I was upset. However, my motto is “Don’t get mad, confirm or reject your suspicions with hard data.”
Battery banks (AKA power banks) seem pretty straightforward. Bigger mAh units should be able to charge a phone more times. However, my research has shown me that there is no real regulation on battery banks, and that it is necessary to go to extraordinary lengths to figure out the true capacity of any unit. These banks are sealed and you often have to destroy them to get a peek at their actual battery. Battery banks can be branded with bizarre sounding names. The seller can silk screen anything that they want to on the case. If a product gets bad reviews it is easy to rebrand the next batch that they are selling. Additionally, the industry itself gives out confusing information making it difficult to know what you are buying even when a company is reputable. Because I review products I had a number of battery banks that were nearly new for testing. I decided to learn more about the ins and outs about these common products; by the end of my research I was not only disappointed, I was shocked.
Some terminology
Ports: Most battery banks have a complement of both USB A and USB C ports. Many (but not all) USB C ports are bi-directional. You can charge the bank through them and they can also output a charge. Some older models may require you to use a micro USB cord to charge, which can be a bit of a hassle as these cords are now less common.
Metering: Most battery banks have some method to tell you how charged they are. Some will have a 4 LED display, while others will give you a more precise digital readout.
Size: Battery banks come in many sizes. Typically, the bigger the bank the bigger the capacity. However, this is not always the case. Make sure that the size that you pick is compatible with your needs. When traveling abroad I had a small battery bank that I could easily slip in my pocket. I was dependent on Google Maps (which consumes a lot of battery energy). I would have been lost without that power bank, which was so lightweight that I barely knew that I was carrying it.
Recharge times: Some battery banks can recharge faster than others. Sometimes that difference can be dramatic.
Watts: Some battery banks will list watts, for instance 15 Watts or 20 Watts on the front of their case. This indicates the maximum watts that certain ports, or a combination of ports can deliver to a device like a phone. Some phones can accept higher watts and will charge faster. Larger devices, like tablets, may require higher watts to trigger their charging circuitry. I tested the power (watts) output of a few banks and their maximum output was lower than what was listed on the case.
Volts Out: Volts refer to the force of the electrical current. Here is a water analogy: If you are trying to fill a bucket it will fill faster if the flow rate is faster (more pressure). Likewise, a battery will fill faster if the voltage is higher. The standard power output of a USB port is 5 volts. However, some phones are capable of accepting higher voltages. and will tell the battery bank to send it. Note that some battery banks can only deliver 5 volts, so that is what the phone will get. Higher voltage output yields faster charging. As an example, an USB C Power Delivery port can (potentially) deliver up to 48 volts. Note, both your phone and the power bank have to be compatible with the same protocol for fast charging to kick in.
Amps Out: Another electrical parameter. This refers to how much charge is moving through the circuit. Using the water analogy, if you filling a bucket it will fill faster if the diameter of your hose is wider. More amps means faster charging. Your phone will limit the amount of amps that it will accept. An old iPhone AC charger will deliver around 1 amp of power, but newer iPhones can accept up to 2.4 amps so an advanced AC charger will charge a phone faster. Some battery banks can provide higher amps, others can’t. A battery bank will usually list the maximum amps that any given port will provide on its case. Here too, I found exaggerations on several banks.
A phone may tell a battery bank to provide more amps; it may also tell a battery bank to provide less amps than the bank is capable of delivering. Exceeding a phone’s charging recommendation can lead to early phone battery failure, and can even cause a battery to explode.
Lastly, a battery providing 2000 mAh at 2 Amps will deplete faster than one providing 2000 mAh at 1 amp. Higher draws have a negative impact on a battery. That is just the way battery chemistry works.
Watts Law: At this point you may be thinking, “What gives, Mike? First you said that higher volts will charge a device faster, and then you said it was higher amps! Which one is it?” The answer is both, as they work together to calculate power, which in this case we are calling watts.
Check out this equation:
volts x amps = watts (power).
When you increase volts or amps (or both) you will supply more power from your power bank to your device. More power means the unit will charge faster.
mAh (milliamp/hour): A unit that indicates overall capacity of a battery bank. One milliamp is equivalent to 1/1000 of an amp. To use the water analogy, think of a battery as a tank. A bigger tank can hold more water and a bigger battery can hold more charge. Common battery bank sizes are 5,000 mAh, 10,000 mAh, and 20,000 mAh.
Depending on the phone, a typical phone battery can store from 2,500 to 4,000 mAh with some phones having batteries that are as large as 5,000 mAh.
A common misperception is that it is simple to calculate how many times a power bank could recharge a phone by doing simple math. For instance, you think that a 5,000 mAh power bank should be able to recharge a 2, 500 mAh battery twice (5,000/2,500 = 2) . To understand why this is not the case we need to get into the weeds a bit.
If you want skip the sciency stuff then go directly to “The Bottom Line”
Most power banks output around 5 volts (some can deliver higher voltages on demand). However, the lithium battery inside the power bank is only 3.7 volts. The mAh listed on the case uses 3.7 volts in its calculation which gives a higher mAh number.
Here is a practical example for a 5,000 milliamp power bank
Volts x amps = watts (Watt’s law again)
3.7 volts x 5,000 mA = 18.5 watts
However, at 5 volts
watts/volts = amps (Watt’s law rearranged)
18.5 watts/5 volts = only 3,700 mA
Note that the overall power (watts) is the same in both equations, but both the volts and amps have changed.
The 5 volt value is (approximately) 75% of what the 3.7 volt value is. This is the case for all power banks. Because of this confusion I think that it is better to compare Wh (watt hours) of a battery bank when trying to figure out its capacity. A typical 5,000 mAh battery will deliver around 18.5 Wh of power. Some well designed batteries may actually give you a bit more power, but still list 5,000 mAh on their case. Other battery banks go in the opposite direction and overestimate their capacity, sometimes to the extreme.
Many Factors Impact A Battery: Let’s assume that we are going to test a quality power bank. There are losses to consider. The power bank has to convert the 3.7 volts of its battery to 5 volts or higher for the USB port. This results in power loss. The receiving device may also have to do some sort of voltage conversion. That could lead to more power loss. Some cheap gas station charging cables have more resistance than branded ones, and you can have a loss there. Most lithium batteries have a BMS (battery management system) circuit. The BMS circuit can do many things. Two of its most important functions are to regulate the voltage used to charge the power bank (too high of a charging voltage can cause a power bank to explode), and to prevent the battery from discharging completely. Completely discharging a lithium battery will dramatically shorten its life. Therefore, the BMS will prevent further discharging once the battery is at 10-20% of its capacity (depending on the programming of the BMS). That last bit of power is not available to the user. Other factors that reduce the power of a battery include the ambient temperature, and the way that the charger is being utilized. Devices that demand a higher amperage to charge will deplete a battery faster, even if it is providing the same mAh as a unit delivering power at a lower amperage.
The Bottom Line
Unless a power pack is over rated it is acceptable to expect that it will only perform at 60-80% of its rated Wh capacity.
Therefore, a typical 5,000 mAh battery that is rated at 18.5 Wh will only deliver 11.1 Wh-14.8 Wh in real life. If a battery has a tested capacity of at least 60% of its listed capacity it is delivering its stated Wh capacity. If it is lower than 60% the seller is telling a fib.
The Test
I needed to come up with a way to drain and monitor a battery bank in a standardized fashion. Luckily, I’m a nerdy guy who has a bunch of electronic tools lying around the house. I came up with two methods. The first method was more sophisticated, and a bit more accurate. However, some of the no name banks could not recognize the first method and would turn off prematurely. The second method was more crude and was slightly less accurate, but it worked for the majority of the battery banks. That was the one that I used. Remember, your results may vary.
The test was simple, I fully charged each battery bank and then completely discharged them using my gadget. I compared the actual power output of a power bank with its stated capacity. If the actual output was at least 60% of the stated output the unit passed. Some packs did very well, others were abysmally bad.
The results
Battery #1 JRT-Japan (however it is made in China) 5,000 mAh pack. This is an exceptionally thin battery that is sexy as far as batteries are concerned. I have had this battery for a year or two, but only use it rarely. It probably has been charged less than 10 times. It claims an output of 18.5 Wh, but only tested at 7.8 Wh, which is 42% of its stated power. Verdict: FAIL
Battery #2 Dilibird.5,000 mAh pack. I could not test this battery using either of my gizmos due to the Dilibird’s limitations. For a crude test I used the battery bank to charge my phone which was at around 60% charge. Even in this situation the pack would randomly shut off and I would have to re-initialize it. Despite all of my efforts my phone only charged to 97% and the Dilibird went from 4 full bars of power to 1 bar. Verdict: FAIL on multiple levels.
#3 Metecsmartme 5,000 mAh pack. The case on this unit is a nice size. It is very pocketable and fairly thin and light. It claims an output of 18.5 Wh and delivered 14.4 Wh which is 78% of stated capacity. Verdict: PASS
#4 4 Meyin Miusc (no that is not a typo) 20,000 mAh pack. This unit impressed me when I did an initial review. However, it is also the unit that performed poorly when I used it at the hotel. It is the reason that I developed this test. The pack is loaded with features, which include a digital power level, wireless charging pad, and multiple built-in power cords. Additionally, it claims 20,000 mAh of power. It did not list Wh (which battery banks are required to do), but a 20,000 mAh battery calculates to 72 Wh of power. In testing the unit it only provided 8.2 Wh of power, which is an abysmal 12% of stated capacity. Verdict: Despite a lot of bells and whistles it falters in its most important property, battery capacity. FAIL
#5 Anker 10,000 mAh pack. This is a fairly slim unit that is easily pocketable. It has outlets for USB C, USB A, as well as a built-in USB C power cord. The USB C outlet is bidirectional. It features a digital power meter. It states that its capacity is 36 Wh of power. In testing it delivered 24 Wh of power, for 67% capacity. Verdict: PASS
#6 6 Veektomix 10,000 mAh power bank. I found this unit in my drawer and added it at the end of my tests (sorry, no photo). This unit is about the same size as the nice Metscmartme, but a bit thicker and heavier. It has a digital display. Ports include a micro USB for charging, USB C which is bidirectional (you can charge here too), and USB A. The small size made me think that this unit overstated its capacity. It claims 38 Wh of power, and delivered 32 Wh, which is an awesome 82% of stated capacity. Best in class. Verdict: PASS
Conclusions
When it comes to power banks it is the Wild West. There is no regulation, and it seems that sellers silk screen whatever values that they want to. Many of the names are bizarre to English hearing ears. It is likely that these brand names come and go so there is little reason for some to establish a quality product.
Expect 60-80% true capacity when buying a decent power bank. However, in my test of 6 units 3 couldn’t even make that level of performance.
Look for a bank with many favorable reviews. Although these can be scammed, it is likely that a well regarded unit with hundreds or even thousands of reviews is legit. Shopping brand names can also help as a company’s future sales can be dependent on present reviews. The Anker unit that I tested passed and is a safe bet, however two lesser known brands performed better. I was especially impressed by the Veektomix. It delivered 82% of its rated power and it did this in an incredibly sleek and compact case.
Lastly, make sure the unit that you buy has the features that you need, including the type of ports as well as the power delivery capability. If you are charging a device that can utilize a higher Amp or voltage output make sure that your unit can deliver it. I think the best units have a bi-direction USB C as well as a USB A port. This combo gives you the most flexibility. If you want a unit for on-the-go use a power bank with a rating of 5,000 to 10,000 mAh should do the trick. Better brands may have better batteries that could offer more charging cycles before they degrade.
Please note that this post is my personal opinion. Testing was done with my available equipment which is not laboratory certified.
Battery Bank and Power Bank refer to the same thing.
Good Luck
Peace
Mike
Addendum: For those interested, I did go try to modify my Amazon review of the Meyin Miusc power bank (#4). I initially gave it a good review as I was impressed by all of its bells and whistles and used it to top off my phone a few times (which worked fine). However, I became aware of its low capacity when I used it in the hotel scenario that I talked about in the first paragraph of this post. When I went back to modify my review the product had been discontinued and was removed from Amazon and so it was not possible to change my evaluation.