Given the fact that the average smartphone battery lasts around 1-2 days at regular use, power banks have become an essential accessory. As they extend the smartphone usage time by multiple days, they enable people to remain connected even when a power outlet is not available.
As they increased in popularity, ever more power bank models reached the market, to the point that it became difficult to choose the best option. At Power Bank Expert, our mission is to help you navigate through the plethora of options available, in order to be able to have all the information that will allow you to know how to choose the best power bank for your device.
Although choosing a power bank is a straightforward task at first sight, it tends to become complicated once you look closer. Before making a decision important factors such as capacity, price, size or charging ports should be carefully considered. We’ll tackle the most important of these aspects below.
mAh (milliamp hours)
Arguably, the most important characteristic of a power bank is its charging capacity. This is measured in mAh (milliamp hours) and it reflects its electrical storage ability. In this sense, mAh is used to describe the total amount of energy a battery can store during a certain time. The higher the mAh, the more energy a power bank can store, and the more times it can recharge your device.
Some of the most common power banks range anywhere from 5000 mAh to 20000 mAh. But as technology improves, power banks will be able to pack more and more energy, going toward 50000 mAh and beyond.
For example, a 5000 mAh power bank can recharge a smartphone with a 2000 mAh battery less than two times. Due to energy losses and battery efficiency, it’s impossible for a power bank to work at 100% output. So the actual capacity of a 5000 mAh is around 3200 – 3400 mAh, close to two-thirds of its advertised capacity. Read more here on the subject of rated vs real battery capacity.
Wh (watt-hour)
Wh represents the amount of power that a portable charger can supply before needing a recharge, and it is another unit to express the capacity of power banks.
However, cell phones and other portable devices are rated in mAh. Thus, it is important to know how to calculate the Wh of your power bank, which is the result of multiplying the nominal output voltage (3.7 V) by the current dissipated by the hour (mAh). For example, the capacity in Wh of a 5000 mAh power bank is 3.7 V * 5000 mAh = 18.5 Wh. A common misconception is to think that the voltage of a power bank is 5 V due to the fact that cellphones charge at this rate, when in fact, lithium.ion batteries have been designed to operate at 3.7 V.
Besides charging capacity, the price is maybe one of the most important aspects that people take into consideration when deciding to buy a power bank. Although it’s definitely an important factor, it can be deceiving if the other aspects mentioned on this page are not also considered.
A cheap power bank might not necessarily have poor built quality, but it may lack some key features such as extra charging ports, it might be heavy and bulky or it may have a low charging capacity.
One of the key metrics we include in our product review pages on the website is mAh/$
1st PBE metric: Affordability (mAh/$)
This is one of the two PBE metrics. These are proprietary metrics to PowerBankExpert.com which we have created in order to help you better gauge the opportunity value of a specific power bank model. In this case, the affordability metric refers to the amount of charging capacity you get per spent dollar. So the higher the mAh value you get for each invested dollar, the better. The average range of this value is around 200-500 mAh/$.
Other aspects that play an important role when choosing a power bank are its weight and size. The ideal power bank comes in a compact size, weighs in next to nothing and also packs a powerful charging capacity. So in order to help you find the best options faster, we have devised a second handy metric:
2nd PBE metric: Portability (mAh/oz – mAh/g)
This metric which is showcased in most of our reviews shows you just how much charging capacity you’ll get per device ounce/gram. The bigger this number is, the more charging capacity that specific power bank packs per mass unit. The most portable power banks pack a high battery capacity (mAh) into a lightweight device.
Although most of the power banks look very similar, they can vary a lot in terms of what’s inside them in terms of charging technology. This is why we cover the most important aspects for each model we review on our site:
High-speed charging
Also known as fast charging, it is a technology that allows high levels of current flow over USB for filling the battery capacity faster, and subsequently reducing charging time.
The voltage and the current are boosted from typical USB rates (5V/0.5A) to produce values up to 100 W of power. Basically, during the initial charging phase, which is known as the constant current phase, a high current is pumped before the battery reaches its peak voltage. This is why fast charging is more efficient when the battery is below 50% of its total capacity. However, the charge controller regulates how much current and voltage a battery can take, and thus, prevent damage.
Many standards in the market offer a faster charging rate. Some of the most common ones are the Qualcomm Quick Charge, and the USB Power Delivery (USB PD), which is the official standard in any device with a USB port. Typical rates are:
- Ø 5V/ 01 – 3 A
- Ø 9V/ 1.67 – 3A (+ 27W laptops and other power devices)
- Ø 15V/ 1.8 – 3A (+ 27W laptops and other power devices)
- Ø 20V/ 2.25 – 3A (+ 27W laptops and other power devices)
However, different manufacturers use the USB-PD standard differently, such as Apple, which supplies 14.5 V and a current of 2 A for a maximum power of 29W, and it’s able to charge iPhone from 0% to 50% in 30 minutes.
Passthrough charging
This technology allows a power bank to charge another device while it is being charged itself. It works under the principle of prioritization, which in essence takes the power being drawn from an outlet and redirects it to the device connected to the power bank.
Passthrough charging provides USB- C ports that can be perfectly used with a wide array of the latest smartphones, as well as other high-power devices. This can be a very useful feature for maintaining your power bank capacity full at all times, but unfortunately, not all power bank models come with it due to safety concerns.
Wireless charging
Some models support wireless charging, which allows phones to get charged by simply being placed on top of the power, eliminating the need of using cables. In order for this to work, however, the smartphone should also support wireless charging.
Wireless charging works by transferring energy through electromagnetic induction. For this reason, a wireless charger uses a copper coil to create an electromagnetic field, which is received by the coil in the smartphone or device. In turn, the receiving coil transforms it into electrical energy to charge the battery.
The Wireless Power Consortium’s Qi standard has been adopted for all the major smartphones and gadgets, including the last version of iPhones, such as the iPhone 8 and the iPhone X. However, one drawback of using wireless charging is that it might take longer to fully charge the battery of your device as it cannot supply as much current as wired connections.
Solar charging
Some power banks come with photovoltaic panels to charge their internal battery, thus supplying renewable energy to charge smartphones and other electronic devices. This is a very handy feature for situations, in which you need power in remote places, such as at campsites.
Some power banks can only be charged by solar power, while others can support both regular charging and solar charging simultaneously; however, it isn’t fast so it might need to be charged through a cable as well.
Another disadvantage of solar power banks is that most of them are manufactured with small capacity, which means they should be used in case of an emergency.
Another crucial aspect to take into consideration is the type and number of ports that the power bank comes with. The last thing you want to happen is to order a power bank only to find out it’s not compatible with your device.
The vast majority of power banks have one or two output USB ports. But even if they all look similar, USB ports are not always the same, as they can have different power values. For example:
- 5V / 1A
- 5V / 1.2A
- 5V / 2A
- 5V / 2.4A
- Etc.
The A value, which stands for Amps, refers to the number of electrons that can travel through the port per second. So the higher the A value, the faster your device will charge. Furthermore, some devices may need a minimum amount of Amps in order to charge. So before purchasing a power bank make sure it’s compatible with the charging requirements of your device.
Charging Cables
Most power banks come with one or more charging cables that can be used to charge the device itself or other devices. Usually, power banks are charged using a micro-USB cable, while the output cables have one of several different socket types:
- micro-USB
- USB Type C
- Thunderbolt
- Lightning connector
An important thing to mention is that although most power banks come with a USB – micro-USB cable for input and output charging, they don’t also come with an actual socket charger, so you might need to use your own cell phone charger.
If you’re planning to take your power bank onboard airplanes, then you should make sure that it’s within the generally allowed limits, which is usually a maximum of 100 Wh without approval. Given that, there’s no universal set of rules that regulate the access of power banks on board planes. This is why limits may vary between different airports, airlines, and countries.
As a rule of thumb, you should have no trouble flying with a power bank that:
- has a capacity smaller than 20000 mAh
- is under 100 Wh
- has a clear label/imprint with its charging capacity (mAh and Wh)
If your power bank does not have all the above checkmarks, you may still be able to travel with it but sometimes you may need to get special permits before being able to board. Some airlines and airports hardly ever enforce these rules, but in extreme situations, you should be prepared to have your device confiscated by airport authorities
We believe that this is an important aspect to take into consideration before purchasing a power bank. This is why we have a metric called “Flight status” on all our reviews.
A device can have one of 4 different statuses:
- Safe: it’s within the most restrictive rules
- Risky: it meets some but not all rules. For example, the power bank can
be under the allowed capacity, but it might not have this information printed on it. This can be problematic
in some international airports. - Special Permit: the power bank is allowed on flights but it will require
a special permit from the airport authorities. - Not allowed: it’s clearly over the allowed limits. You won’t be able to
take this device on any flight.
For more information on this subject, including the official FAA, IATA, and TSA rules, check out our dedicated article on this subject.
Power indicator
Most portable chargers have an LED power indicator which reflects the current charging capacity of the battery. This is a very useful feature as it allows owners to see when the battery is low on capacity so that it can be recharged as needed.
LCD Display
Advanced models include a small LCD display. This is a fancier LED indicator as it can display the percentage of charge capacity. Instead of 3 out of 4 LED lights, you get 75%. This is a more accurate way to tell just how much charge is stored in the device. Some power banks even feature both a LED indicator and an LCD display.
Shortcircuit safety
This is somewhat of a standard feature. There are very few models that do not have some type of short-circuit safety. As you may guess, this feature prevents power banks to shortcircuit and cause various hazards such as fires or device malfunctions.
Adaptors
Some power banks come with an array of adaptors so that it can be easily used on various types of devices. Adaptors increase compatibility if you happen to have multiple devices which have different types of input ports. For example, a power bank with an adaptor set would allow you to charge a phone that uses a micro-USB port but also an iPhone that uses a Lightning connector.
Protective pouch
Somewhat of a common feature, a protective pouch can be useful for transporting and storing your power bank. Although some people might find this a useful item to use, in all honesty, most users won’t bother to keep their devices in the protective pouch.
Flashlight
Many power banks come with a built-in LED flashlight, which can be a nice bonus feature. This might come in handy in various situations such as in the middle of a blackout.
