# Everything You Need To Know About Power Banks. Power bank output voltage

## Everything You Need To Know About Power Banks.

Power Banks have become an essential item for all smartphone users. Still, there are a lot of things about a power bank that most of us do not know.

I am going to cover everything there is to know about a power bank.

## Power Bank Capacity (Paper Vs Practical)

Power Banks come in different capacities. The capacity that a manufacturer has written on the power bank vs the actual capacity that we get is different.

It is not that manufacturers are lying to us and writing a different capacity. It is the same marketing strategy that everyone uses these days to make their products look better on paper.

If a power bank capacity is 10000mAH, it does not mean the power bank would charge a 2500mAH smartphone battery four times. In practice, even a really expensive or high quality 10000mAH power only charges a 2500mAH smartphone around 3 times.

The question is why is the power bank capacity different in actual use?

The thing is, a power capacity of 10000mAH or so is rated on 3.7V. This means that cells insides the power banks have 3.7V. But our smartphones are charged at 5V at least. Also, the efficiency of a good quality power bank is around 90%. Let’s do a rough calculation, [(3.7/5)x100]x0.90=66.6% This is why most people say that the power bank’s real capacity is around 66.6% or 2/3 of the written capacity. So a 10000mAH power bank charging a smartphone at 5V would have 66.6% of 10000mAH= 6600mAH.

If we were fast charging our smartphone at 9V, the calculation would be [(3.7/9)x100]x0.9=37%. The capacity of 10000mAH power charging a smartphone at 9V would be 37% of 10000mAH= 3700 mAH.

The unit mAH stands for milli-Ampere-Hour and it represents the charge stored. A milli=1/1000, so a 10000mAH power bank would be 10AH (10x1000mAH, 1A=1000mA).

1 AH, or 1 Ampere-Hour simply means, at the rated voltage (3.7V) of power bank, it could provide 1 Ampere current for one hour. So 10 AH or Ampere-Hour, power bank could provide 10 Ampere current for 1 hour or 1 Ampere current for 10 Hours. It works both ways, 1×10 AH or 10×1 AH, 1Ax10H (1 Ampere for 10 hours), 10Hx1A (1 Ampere for 10 Hours).

But due to the voltage difference for which a power bank is rated at (3.7V) and the voltage our smartphones charge at (5V or 9V), the mAH changes. The mAH is dependent on the output voltage.

This is why mAH is not an accurate way of determining a power bank capacity. The other unit we can rely on is WH or Watt-Hour and the smaller unit is mWH or milli-Watt-Hour. Watt, the unit of power, is dependent on both voltage and current. Watt-Hour or WH represents energy stored and is actually used to determine the capacity of a laptop battery. Watt-Hour or WH is not dependent on voltage.

But if a power bank is rated at 10WH, you can expect a power of 10 Watts for one power or power of 1 Watt for 10hours. We do not have the problem of different voltages now. But the thing is only a handful of power banks has their capacity written in Watt-Hour. But most of them have mentioned the capacity in WH in their user manuals.

The solution is then to look at the official specification of a power bank and calculate the capacity ourselves. I will show you how. Look at the picture of Anker power bank from the official website.

It is a 10000mAH power and it can charge 3.5 phone charges? I tried to look at the manual on the internet of this specific model and I found the capacity.

The instruction manual shows the capacity as 36Wh or 36 Watt-Hour. We need to convert this to mAH. We know that the rated voltage of every power bank is 3.7V and we need the power bank capacity at 5V.

So, the 36Wh or 36000mWh/5V= 7200mah. But no power bank has a 100% efficiency. Assume the efficiency is 90%, the capacity would be 7200×0.8=5760mAH. The 80% efficiency is normal for brands like Anker, Mophie, Xiaomi, and Aukey, etc.

Note: The efficiency reduces when you are fast charging a device due to excessive heat.

Another example is the Xiaomi Power Bank.

Xiaomi is really good at giving out the exact specifications of their power banks, unlike Anker. It says that the Xiaomi 10000mAH power bank can charge 3.5 times an iPhone 7.

iPhone 7 capacity is 1960mAH x 3.5=6860mAH. This is the real capacity of this Xiaomi Power Bank at 5V.

The conversion rate of up to 90% does not mean that the efficiency is up to 90%. on this later.

## Power Bank Quality

Power Bank Quality is just as important as its capacity or quantity. Power Bank Quality is dependent on a lot of factors.

High-Temperature Protection: The heat produced by the power bank while charging a smartphone should as little as possible. Normally a power bank would heat up for sure while charging. If the power bank becomes hot enough that you can not touch it comfortably at room temperature. The power bank is of low quality. If a good quality power heats up more than the recommended range of temperature, it will turn itself off for some time to reduce temperatures. The safe temperature range for a power bank is between 5 °C and 40 °C.

Power Bank Efficiency: A higher efficiency power bank is always better. A good power bank has efficiency above 80% when charging at room temperature. Higher efficiency means the power bank delivers power to the connected devices with little losses. Higher efficiency also means a higher power conversion rate.

Power Bank charge cycles: A good quality Li-Po or Li-ion battery used in power bank have around 500 charge/discharge cycles.

Charge Hold: If you charge your power bank and do not use it for a long time. Good quality power banks can retain the charge for about 3-5 months while a cheap quality power can retain the charge for only about 1-2 months.

Input and Output Overvoltage Protection: This ensures that the device does not get more voltage than required for charging. A higher voltage can damage a device.

Protection from the short circuit: If you try to charge a power bank with itself by connecting the cable to input and output terminals of the same power bank, a cheap power bank would short circuit, leak and may even explode. To avoid this, good quality power banks have short circuit protection. Power bank cuts off the connection to avoid any short circuit. This also helps, if you throw some water into the USB port of power bank or if you put your power bank in the along with a metal object.

Overcharge Protection: When a smartphone battery is full, the power bank would automatically turn off the connection to avoid overcharging the device, This is why you can leave your smartphone connected to a good quality power bank overnight without any problem.

Voltage Regulation: The better the voltage regulation of a power bank, the less it will deviate from the rated voltage. Better voltage regulation means stable output voltage which is essential to keep a device safe and also essential for a good quality power bank.

## Does Power Bank Damage Smartphone Battery?

Power Bank can damage a smartphone if it is providing the output voltage less than smartphone rated voltage or more than the smartphone rated voltage. Power Bank needs to provide the voltage in the range that is safe for the smartphone.

Power Bank will damage your smartphone if the output voltage of the power bank is higher than 5.4V or lower than 5V. This is because our smartphones are compatible with voltages between 5-5.4V. You can check the output voltage of your power bank by using a multimeter. It can be measured by taking a multimeter and holding its probes between the two end metallic strips on the USB port of power bank.

If your power bank has an output voltage above 5.4V and you need to use that power bank in case of an emergency. You should use this power bank to only charge a smartphone up to 60% and not more than that to avoid damage to your smartphone battery.

A really good quality power bank has an adaptable voltage. Due to this, a power bank can change the output voltage depending on the device connected to it. This power bank would not damage your device.

This is probably the most asked question about a power bank. If this is confusing to you, do not worry.

The output voltage of a power bank is not just one fixed number, it fluctuates between different voltages. This is the role of a voltage regulator to keep the voltage stable with very little fluctuations. This is why I said earlier voltage regulator plays an important part in determining the quality of a power bank.

To be honest, every good quality power bank has a good voltage regulator these days. So you do not need to worry about this.

So to sum it up, if you have a good quality power bank that is not more than two years old, it will not damage your smartphone. But if you are not sure of the quality of the power bank or you have a cheap power bank, it will damage your smartphone battery.

If you have an old power bank, it is not necessary that it will perform worse or damage your battery, I have just given an approximate time based on my usage and survey.

A power bank is always inferior to a regular wall charger. Just think about it this way, we have to pay 20 for a wall charger which provides 18W charging. A power bank of 10000mAH from Xiaomi also costs 20 and also provides 18W fast charging. Can you really expect the same quality charging circuit from both of these chargers? Nope.

What I found was, as the power banks get old, depending on the usage. The power bank has a lot of wear and tear which causes it to produce an abnormal amount of heat when charging. Also, the voltage fluctuation increases with time, which is not good for any smartphone.

## Power Bank Special Features

There are some features that make an expensive power bank worth its price. Every power bank manufacturer has at least two power banks in the same capacity. One with only basic and important features. The other full of extra features at a higher price.

If you need those features or not depends totally on your usage and budget. I am going to explain all of those features here.

It is simple, if you buy a cheap power bank, you would not get any features because it is not possible at a low price. Then you have power banks that cost normal and have an adequate amount of features for most users. At the end of the spectrum, you have some power banks which include exclusive features but comes at a higher price.

Low Current: Only Pro or elite versions of power banks can provide currents in the range of 50mA or below. Xiaomi Mi Pro power banks cost around 1.5x the price of standard power bank but it has this low current feature.

As you can see, low current is required to charge some of the devices like Smart bands and wireless accessories. This feature is not available in every Anker power bank too.

Power Cut Off: This feature should be in every power bank. Still, only a few power banks by each manufacturer have this feature. What it does is cut off the power, when the smartphone battery is full. This way, you do not have to worry if you leave your smartphone attached to the power bank for a long time. When you are charging the power bank itself, Power banks also cut off the power to the wall charger. This feature is normally called overcharge protection.

Pass Through Charging: While your power bank is charging, if you plug your smartphone into the power bank output port, your smartphone would charge too if your power bank has ‘Pass Through Charging’ feature. I love this feature. Once I charged my two power banks and my smartphone in one night because I had to go to a trip next day. I connected one Mi power bank to wall charger, 2nd power bank to first power bank output port and my smartphone to 2nd power bank output port. This feature is not available in most of the power banks.

Adaptable Voltage: Some power banks support 5V, 9V, and 12V charging. This way the power banks can adapt to any voltage levels depending on the requirement of the connected device. This feature is also exclusive to premium versions of power banks. Standard power bank only supports 5V 1A and 5V 2.4 for each port.

Let’s just look at the specifications of 26 dollars power bank vs 44 dollars power bank with the same capacities from RAVPOWER.

LEFT: 26 Prime power bank, Right: 44 PD pioneer power bank

The prime power bank (26) only supports 12W max output with 5V/2.4A while the PD Pioneer power bank(44) has three different adaptable output voltages 5V/3A, 9V/3A, 12V/2A, 14. 5V/2A and also supports 18W charging for the main port. The PD pioneer power bank also supports PD(Power Delivery) charging.

The expensive power bank also supports 18W charging for input.

Higher Efficiency: The pricey power bank from a same company has higher power conversion rate and efficiency. Let’s take Xiaomi for example (it is one of my favorite brand for accessories), they have a standard power bank which has around 80% real life efficiency and theoretical 90% efficiency. The pro power bank from Xiaomi has 93% theoretical efficiency and around 87% real life efficiency. The higher efficiency power banks also lasts longer. I will explain the efficiency in detail later on in this article.

## How To Use a Power Bank Correctly

There are few things you need to keep in mind to use a power bank correctly and extend its lifetime.

• Charge before first use: When you buy a power bank, charge the power bank overnight before using it.
• Charge Every three months: If the power bank is not in use, you should charge a good quality power bank at least once every three months. For a cheap quality power bank, charge it after every 4-6 weeks.
• Charge The Right Way: Just like any other battery, it is better to charge the power bank between 20% and 80% to prolong its life span. If you must charge your power bank to 100%, at least do not let it get below 10%.You would run out of 500 cycles very quickly if you do not take care of your power bank. My last Xiaomi power bank lasted 4 years with heavy use because I didn’t get its charge below 10%.
• Keep the Power Bank Cool: If you are charging any device with power bank, it will get hot which is fine. But when you play games on your smartphone when it is connected to the power bank, power bank has to provide maximum output power which in turns heats up the power bank. The more heat any electronic device produce, the shorter the life span would be. So do not play games or intensive tasks when charging your smartphone. Also do not forget your power banks in your car or hot places because it might explode in direct sunlight.
• Avoid Metal Objects: Most of the power banks have short circuit protection. But still do not put the power bank in with a metal object. Better safe than sorry.
• Small Cable: Use a small cable for charging because a smaller cable has fewer losses. Less losses means more efficiency. It is fine to use a lengthy cable if you need to. But the power conversion rate would be reduced because a lengthy cable has a lot more resistance than a small cable. This is why power banks are shipped with smaller cables.

## Power Banks Efficiency:

Power Banks efficiency varies for each power bank. The higher the efficiency of a power bank, the more output power it will be able to provide based on the rated capacity.

If a power bank has 10000mAH at 3.7V and has an efficiency of 90%, the output capacity will be 9000mAH at 3.7V only. The efficiency and capacity would change at 5V which we normally charge our smartphones at.

Similarly, if you were charging your smartphone at 9V. the efficiency would decrease significantly. The thing is, charging at higher volts means a lot more power has to be passed through per second which produces extra heat. Heat reduces efficiency.

The cells of a power bank are at 3.7V. When the power bank has to charge to smartphone, it has to convert the 3.7V to 5V, this conversion is called Power Conversion. This conversion causes energy losses. The higher the voltage you need to convert to (e.g. 3.7V to 9V). the more energy losses there would be. This is why fast charging is not recommended on a power bank to get a good efficiency.

## Power Banks Recommendations:

There a lot of power bank companies out there. I will only list the companies of power banks that I know and trust.

You can buy power banks from any of these companies, these are reputable brands and offer warranties.

The Names and Amazon links to the Power Banks I recommend are given below:

## How to Prototype a Power Bank Charger Without Building Any Dedicated Hardware

The short answer to this question is yes, and, as this question has been asked by many customers over the years, this article was written to explore the topic in further detail. This article will review the process involved in developing an application using existing evaluation boards, discuss the challenges encountered, and outline recommendations for further revisions and improvements.

### Introduction

Ideally, any power supply design should start with some basic proof of concept tests, which often involve testing an existing demo board. This demo simply takes this preexisting step (of testing single rails on the demo hardware) and expands on it to produce a working system using demo hardware. Furthermore, as this demo was needed within a relatively short time frame, the typical development process of design, layout, build, assemble, and test (plus any design iteration) was not possible, so the system was prototyped in its entirety using nothing but readily available hardware.

### Application

To answer the question posed at the beginning of this article, it was necessary to choose a high level application as a starting point to prove this was possible. This led to the power bank charging application being selected as a proof of concept. As power management is a prerequisite for every electronic project, any other application could have been selected.

A power bank charger is a common enough application, which most consumers have encountered and used—for example, many travelers carry one to ensure their phone remains charged over a long journey. A power bank is essentially a battery pack (capacity varies depending on the price and range required), with one or more USB-A ports as well as a USB-C input port to charge it. It is possible of course to layer additional complexity on top of this basic functionality—for example, the addition of a wireless charging pad or an input to allow solar charging of the bank for outdoor enthusiasts.

For this application, the option to charge the battery via solar or to charge via a DC input from a standard 12 V AC-to-DC wall wart was included. The outputs included some basic USB-A charging ports (two in total), producing 5 V for use with mobile phones and a range of USB-powered electronics.

### Power Source Selection—LTC4416

In this example, the design will support two input power sources (a solar panel and an AC-to-DC wall wart, which is just a simple AC-to-DC power supply). For this reason, a clever device called a power path prioritizer is required not only to intelligently switch between the available sources depending on which was available but also to manage the situation where they both were available by assigning priority to one source or the other. A simple version of this implementation can be achieved by using some simple diodes—commonly connecting the two cathodes of the diodes and connecting the anodes to their respective sources. Unfortunately, this particular configuration is lossy due to the diode drop inherent in a typical diode (approximately 0.6 V), but it also doesn’t allow for any clever selection criteria to be implemented, for example, priority selection. It simply allows the higher potential input to pass through.

Here LTC4416 comes into play—it not only replaces the lossy diodes with PFETs, which are far more efficient, but also allows for priority to be assigned. In this particular application, priority will always be assigned to the wall wart. This allows the design to take advantage of the available power (and higher current) when it is available. This device is exceptionally flexible, with many operational modes possible depending on the design requirements. Table 1 (sourced from the LTC4416 data sheet) displays the modes of operation.

Table 1. Modes of Operation from the LTC4416 Data Sheet

 E1 E2 Operation Mode IG(OFF)1 IG(OFF)2 1 0 Load sharing Enabled Enabled 1 Sense V1 is less than V2 Enabled Sense 0 V1 is greater than V2 Enabled 0 X Channel 1 disabled Do not use Disabled X 1 Channel 2 disabled Do not use Disabled 0 1 Both channels disabled Disabled Disabled

### Switching Buck Battery Charger—LTC4162-L

For the battery charger, the LTC4162-L was selected due to its wide input voltage range (up to 35 V) and 3.2 A charging capability, as well as the integrated FET design, which results in a small solution size. This is a commonly used, full-featured charger IC, which has great application flexibility as it comes in many battery chemistry variants such as LiFePO4, Li-Ion, lead acid, etc., as well as an I 2 C interface to allow the user to extract telemetry information. It was selected for this particular application not only because of the aforementioned flexibility on the input and battery voltage but also because of the integrated nature, which helps to keep the solution size to minimum. Another useful feature that it has is maximum power point tracking (MPPT)—if solar is one of the possible input sources for your design, MPPT is a must to ensure the design extracts as much available power as possible. The LTC4162 also has a built-in power path control that is useful in this application when the input source is removed, allowing the provision of the battery voltage to the output terminals for use downstream.

### USB Charging Solution—CN0509

The board selected to provide the USB charging voltage for the connected device is from our Circuits from the Lab collection of reference designs and solutions. Typically, a single device is shown on an evaluation board to allow evaluation of that specific device. Circuits from the Lab boards, however, are a more solution-focused implementation that makes use of several Analog Devices’ products from different product portfolios to solve a particular system requirement.

The CN0509 was designed to be a wide input range, dual USB power charger. It was developed for use in emergencies such as natural disasters or extended power outages. An example power source that many would have available to them is a car battery. This board can be powered by a car battery to provide two 5 V ports, which are isolated from the primary voltage for safety. There is a range of alternative power sources that you may have available from stacks of loose batteries to motors to act as a simple generator. The CN0509 has a wide input voltage range so it will be able to run from any supply in the range of 5 V to 100 V. For all of the above reasons, this makes it an ideal candidate to pair up with the existing boards to provide the USB charging outputs required for the power bank charger.

Reverse polarity protection is included to protect the circuit from an incorrectly connected supply and an isolated flyback converter is utilized to isolate the charger outputs from the input source—this is particularly useful if a –48 V communication backup supply is used as a power source. This can result in a phone being charged to –48 V and creating a hazardous situation. Isolated conversion prevents this from occurring. Another note here is that the CN0509 board is quite small; much of this is attributed to the highly efficient ICs selected and the no-opto flyback LT8302. A key differentiation is that the flyback converter LT8302 does not need an isolated optical feedback path.

There are two USB ports on this particular board: one is a standard USB port (without D/D– connected) and the other port has a DCP controller to monitor the USB data line voltages so that it can enable fast charging and provide 5 V at 2 A max. Achieving this higher level of charge current is dependent on the input voltage utilized. 12 V is optimal based on the performance graph shown in Figure 4.

### Power Sources

The primary power source selected was a 60 W AC-to-DC 12 V adaptor. This served as one input to the LTC4416 demo board, and a relatively small solar panel was purchased to provide an alternative input source—since this project was to be used at an indoor event and there was never going to be sufficient lighting available to provide a reasonable level of available power to run from solar, this feature was included simply to demonstrate the capability and functionality of the power path prioritizer.

This particular design was developed to be a power bank and as such it would require a battery pack to act as the storage element. Shipping restrictions in relation to batteries are prohibitive. The demo was developed specifically so that a generic battery pack could be bought and inserted to run the demo on its arrival. Based on this limitation, a rechargeable 2× series cell Li-Ion battery pack generating a nominal 7.4 V with a 2600 mAh capacity was selected to run the demo for the event. It is worth noting that a larger capacity battery could easily be installed here if required.

### Demo Build

From a build perspective, the hardware was standard, so no electrical modifications were required beyond some adjustments of the LTC4416 thresholds to ensure the correct priority for the input power sources. In order to make it more visually appealing for the event, the boards were mounted on a simple black Perspex sheet using some standard metal standoffs.

The charge current that was being provided for the evening was monitored by a simple USB meter. This device visually represented how much current was available to charge the attendee’s phones.

### How It Performed

The demo performed its core function effectively; it comfortably charged the battery pack from two alternate sources, the handover between sources was managed well by the power path prioritizer, and the CN0509 nicely provided charge to the connected USB devices. This particular power bank has another useful feature that many power bank chargers do not have and that is the ability to simultaneously charge the battery pack and charge the connected USB device. For example, my power bank, which many would consider reasonably high end, will not charge the phone and the bank itself at the same time, which is a frustrating limitation.

The charge current to the USB port is limited by the capability of the LTC4162 with its internal FET design providing a max of 3.2 A—the bulk of the current is sent to the battery during charging. The remaining current can be used through the USB charger ports.

Any time the input power source is removed, the power path FET on the LTC4162 demo board ensures that the battery power is redirected to the output port and hence maintains power to the CN0509 and USB ports. The available charge current in this mode drops as per the graph in Figure 4—since the input source to the CN0509 is now the battery voltage, which is a nominal 7.4 V.

### Next Steps

Once the application has been proven to work using some simple, readily available demo boards, the next reasonable step is to develop a product prototype that takes learnings from the initial prototype work and integrates this into the end solution. Part of this would be to modify the existing schematics from the boards used to remove the superfluous items (test points, connectors, etc.). The user could then get started on the PCB development, which would then show off the importance and usability of the resources we provide with each of our devices. For example, the optimized demo board layout is a freely available resource provided for each of our devices. While the demo board generally looks to be quite large in size, this is simply to aid the testability and usability of the device. Closer inspection of the board layout reveals that the IC for which the board was developed and the enabling circuitry (resistors, capacitors, inductor, etc.) are all designed into as small a space as possible to allow customers to bring this into their own layout. This will then provide confidence to the customer as they know that this is a tested design, which they can verify on the bench before building their own version.

For the end application, a larger capacity battery with a higher voltage would help to optimize the amount of charge current provided to the USB ports.

The CN0509 is a fantastic design and fulfills its requirements perfectly; however, for this particular application, a more slimmed down design could be utilized to reduce the overall battery bank cost. For example, the LTC7103 and input polarity protection circuitry would not be necessary for this design and the isolated flyback could be powered directly from the output of the LTC4162 (either 12 V from the AC-to-DC wall wart or the battery voltage once mains power has been removed).

### Conclusion

You can certainly prototype a power bank charger, or any other power supply design for that matter, using some readily available hardware and simple power sources. This highlights that using available demo board hardware can quickly provide a proof of concept for potential projects without spending much on development. Furthermore, this relatively small but valuable step will provide the user with confidence before committing to a more integrated design. Another point worth reiterating is that power supply design and, more specifically, the layout of a power design can be challenging so it is worth utilizing the resources available to reduce the overall development time.

### Author

Diarmuid Carey is an applications engineer with the European Centralized Applications Center based in Limerick, Ireland. He has worked as an applications engineer since 2008 and joined Analog Devices in 2017, providing design support for the Power by Linear portfolio for European broad market customers. He holds a Bachelor of Engineering in computer engineering from University of Limerick.

## Power bank output voltage

Power banks have become an essential accessory for people who rely on their mobile devices throughout the day. But have you ever wondered why the real capacity of power banks often differs from the advertised capacity? In this blog post, we’ll explore the reasons behind this discrepancy, including the difference between battery voltage and USB voltage, and showcase our fantastic collection of high-quality power banks with warranty from popular brands like Anker, Energizer, Matrix, and Cager.

### The Voltage Difference: 3.7V Batteries vs. 5V USB Standard ⚡

One of the primary factors contributing to the difference between the real capacity and the advertised capacity of a power bank is the voltage difference. Power banks have built-in 3.7V batteries, which are the backbone of their energy storage. These modern, slim power banks often contain thin lithium polymer batteries that maintain a 3.7V standard while being compact in size.

However, the USB standard for charging is 5V. Inside the power bank, there is a conversion circuit that changes the 3.7V output from the batteries into a USB-friendly 5V. When converting to a higher voltage, the capacity (mAh) must also be adjusted to match the new voltage.

To calculate the theoretical USB output capacity, you can use the following equation: ACTUAL 5V mAh = 3.7 x Advertised mAh / 5.

For a 10,000mAh powerbank 3.7 X 10,000 / 5 = 7,400 mAh, meaning it can supply 7,400mAh at the 5V USB connection. This results in a 23% reduction in the stated capacity of the power bank right out of the box.

### Energy Conversion Efficiency: Another Piece of the Puzzle

Another reason for the difference between the advertised and real capacity of power banks is energy conversion efficiency. When a power bank charges a device, some energy is lost in the form of heat during the conversion process. This means that not all of the stored energy is available to charge your device.

Typically, power banks have an energy conversion efficiency rate between 70% and 90%. For example, if a power bank has an advertised capacity of 10,000mAh and an energy conversion efficiency of 80%, its real capacity would be around 8,000mAh. This is because 20% of the energy is lost during the conversion process.

### Other Factors Affecting Power Bank Capacity

Besides energy conversion efficiency and voltage differences, other factors that can impact the real capacity of a power bank include:

• Battery degradation: Over time, the capacity of a power bank’s battery will decrease due to regular use and charging cycles.
• Temperature: Charging a device or power bank in extreme temperatures can also reduce its efficiency and capacity.
• Device compatibility: Some power banks may not support the optimal charging current for specific devices. This can lead to a lower output capacity when charging that device.

### Choosing the Right Power Bank for Your Needs ⚡

When choosing a power bank, make sure to look for the following features:

• Quality materials and components: Power banks from reputable brands like Anker, Energizer, Matrix, and Cager are known for their durability and performance. They use high-quality materials and components to ensure optimal efficiency and capacity.
• Warranty: A warranty is a sign of trust and confidence in the product. Our power bank collection comes with a warranty, so you can be assured of their quality and performance.
• Capacity: Choose a power bank with a capacity that meets your needs. Consider how often you’ll need to charge your devices and the types of devices you’ll be charging.

Ready to find the perfect power bank for your needs? Check out our fantastic collection of power banks from popular brands like Matrix and Cager. Get ready to stay charged and connected, no matter where your journey takes you!

## The Best Portable Chargers and Power Banks for 2023

Is your phone, tablet, or laptop typically in the battery red zone before the day’s end? These portable chargers and power banks give you the most boost when you’re out of juice.

I love portable technology—if you can put it in a or a bag, I’m probably into it. I’ve covered phones and tablets of all shapes and sizes, and reviewed everything from game consoles to laptops in my decade-plus career. Prior to joining PCMag, I wrote articles for Android Authority, How-To Geek, MUO, New Atlas, Tom’s Hardware, and plenty of other tech publications.

Apple MagSafe Battery Pack (Credit: Steven Winkelman)

Watching your phone or tablet steadily run out of power when you’re nowhere near an outlet is stressful. Fortunately, third-party portable batteries are available in many sizes and capacities. Some power banks offer fast charging, wireless charging, built-in cables, AC adapters, and LED flashlights—and even the ability to jump-start your car. Regardless of your budget, you can find a portable charger that keeps your device going when your battery icon starts to dip into the red.

But with so many options to choose from, how do you know which one is right for you? Read on for our tips, followed by the most important points to consider as you shop.

### Recommended by Our Editors

Best Affordable PD Power Bank

## Anker PowerCore Slim 10000 PD

### Why We Picked It

Despite its reasonable price, the Anker PowerCore Slim PD 10000 offers high-end features like USB Power Delivery for fast charging, as well as both types of USB ports.

### Who It’s For

This 10,000mAh charger doesn’t have the highest capacity, but it’s more than enough for people who need just a little extra power throughout the day and don’t have the patience for slow charging speeds.

Best Ultra-Portable Power Bank

## Anker 321 Power Bank (PowerCore 5K)

### Why We Picked It

A huge battery capacity is convenient, but sometimes you need a small device that you can carry around without a backpack. The 5,200mAh Anker 321 Power Bank fits that need perfectly, especially because it offers both a USB-A and USB-C port.

### Who It’s For

This is ideal for people who care more about portability than capacity. It won’t charge your phone multiple times, but it can still get you through a long day.

Best for Charging Laptops

## Anker 737 Power Bank

### Why We Picked It

The Anker 737 features 140W output, which means it can charge bigger, more power-hungry devices like a laptop just as effortlessly as it can juice up a phone or tablet.

### Who It’s For

If you often need to charge a laptop when you’re nowhere near an outlet, this 24,000mAh backup battery can lower your stress levels. It’s more expensive than other options on this list, so people who tend to charge smaller devices like phones or tablets are better off with the more affordable choices.

## Apple MagSafe Battery Pack

### Why We Picked It

True to its name, Apple’s MagSafe Battery Pack is notable for its MagSafe support. You can simply stick it to the back of your phone to charge it wirelessly.

### Who It’s For

If you need to keep your iPhone running while away from home, you won’t find a more convenient solution. People with older iPhones (before the iPhone 12) need to look at other options, though, as MagSafe isn’t supported.

Best High-Capacity Power Bank

## Mophie Powerstation XXL

### Why We Picked It

The Mophie Powerstation XXL does it all—it has a considerable 20,000mAh capacity, 18W PD charging, and both USB-A and USB-C ports.

### Who It’s For

If you’re looking to recharge a phone or tablet several times on the go (and quickly), this is a top choice. The only drawback is that it doesn’t support larger devices like laptops.

Most Durable PD Power Bank

## Otterbox Fast Charger Power Bank

### Why We Picked It

Many people know Otterbox for its durable phone cases, but the company is now bringing that expertise to the world of power banks. In addition to its strong build quality, the Otterbox Fast Charger Power Bank has all the key features you need, such as fast charging with PD, both types of USB ports, and several options for battery capacity.

### Who It’s For

If you are worried about damaging your backup battery when you travel or commute, this is one of the safest bets. It also comes with a limited lifetime warranty.

Best Solar-Powered Portable Charger

## QiSa Solar Charger

### Why We Picked It

The QiSa Solar Charger can use the sun to recharge itself, supports both wired and wireless charging, and even has a built-in flashlight. Best of all, it offers a massive 38,800mAh capacity.

### Who It’s For

If you spend a lot of time outdoors, this is among your best choices for keeping your devices running while off of the grid. In other words, it’s camping approved.

## What Size Battery Do You Need?

On the.friendly front, most smaller batteries have a capacity of around 5,000mAh, which is typically enough to top up most phones once.

Meanwhile, a 10,000mAh battery can give today’s flagships two full charges. A 20,000mAh battery can charge a flagship four times, or two phones two times. Some power banks have enough juice to power laptops. Of course, a higher capacity often translates to a heavier, larger, and more expensive battery.

Most companies advertise how many times their products can recharge popular phones, but if you want to calculate that number for yourself, RAVPower has a useful guide (Opens in a new window) that can give you an estimate.

In the end, it’s best to assess your typical needs before buying. If your phone hits the red zone by mid-afternoon and you only need enough juice to get you to the end of the workday, a 5,000mAh battery should be plenty.

## What’s the Difference Between Power Input and Output?

You’ll find three types of ports on today’s portable batteries:

Generally speaking, you charge the battery itself via micro USB or USB-C (input). Some batteries charge faster than others and USB-C charges much faster than micro USB.

Nearly all batteries include a standard USB-A port (output). This is for plugging in USB-A-to-micro-USB, USB-A-to-Lightning, or USB-A-to-USB-C cables for charging your iPhone or Android device.

Some batteries include built-in output cables and these generally have micro USB, USB-C, or Lightning connectors.

The most important thing to do is to match the battery’s output to your phone’s input. For example, if you have an iPhone, be sure the battery has its own Lightning connector or supports USB-A-to-Lightning or USB-C-to-Lightning cables.

Larger batteries with higher capacities might include a multitude of ports to support input and multiple outputs at the same time. You may see two USB-A and two USB-C ports, for example, though micro USB ports are becoming less common.

If you picked up an iPhone 13 or iPhone 14 and were surprised by the lack of an included wall charger, see our article on charging your iPhone.

## What Is Fast Charging?

Another factor to consider is how quickly a power bank can charge your device. Battery output is measured in voltage and amperage. Amperage (or current) is the amount of electricity that flows from the battery to the connected device, while voltage is the amount of potential energy. Multiplying volts by amps gives you wattage, the measure of total power. To make devices charge faster, most manufacturers either vary the voltage or boost the amperage.

Today’s devices support a wide range of Rapid-charging technology, such as Qualcomm QuickCharge, USB Power Delivery, or proprietary fast-charge systems.

Quick Charge works by increasing voltage rather than amperage. This standard typically allows you to charge supported phones to 50 percent capacity in 30 minutes, which is especially helpful when you need power in a pinch.

Power Delivery is a newer protocol in which two compatible devices negotiate on the fastest charging option available based on the charger, cable, and circuitry. It also allows for power to flow both ways.

The most common devices (Apple iPhones and Samsung Galaxies) support charging rates of 27W and 45W, respectively. It’s best to look for batteries that can support charging in that range.

## Is Pass-Through Charging Safe and Useful?

Pass-through charging is another feature to consider; with it, you can charge devices and the portable power bank simultaneously. That’s convenient if both your phone and backup battery are running on empty. You shouldn’t encounter any safety issues if the manufacturer of the portable battery you buy advertises pass-through charging as a feature, but the power output might change in this mode.

## How Does Wireless Charging Work?

Wireless charging has become popular because it allows you to power up compatible devices without a cable. Qi is the dominant standard for compatible Android phones (up to 18W) while Apple iPhones rely on MagSafe charging (up to 15W). iPhones will charge wirelessly on Qi chargers, but only at 7.5W.

Some battery makers have built Qi or MagSafe-compatible wireless charging into the surfaces of their portable batteries. Such batteries mean you can leave the cables at home.

## Should You Buy a Battery Case Instead of a Power Bank?

If you find that you often forget to carry your backup battery when you need it most, you should consider a dedicated battery case instead. These combine the portability and protection of a case with additional battery capacity to keep your phone topped off at all times.

There are several drawbacks. First, they have limited additional capacity on board. Second, they are limited in terms of the number of phones they support (mostly just iPhones, Galaxies, and Pixels). Third, you can’t charge much else with them.

## The Best Wireless Chargers

Why fumble around for a charging cable when you can rest your phone on a wireless charging pad? Whether you’re an Android user or an iPhone fan, check out our roundups of the best wireless chargers and the best MagSafe chargers to help you cut the cord.

Steven Winkelman contributed to this story.