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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.

Let’s Start.

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.

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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.

Anker Powercore 10000mAH manual

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%. More 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.

Some of the factors are:

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 pocket along with a metal object.

Adaptable Voltage: Good quality power banks are compatible with every device. These power banks have adaptable voltages. This is why a power bank can charge at 5V as well as 9V depending on the connected device.

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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.

Let’s list the features:

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.

Xiaomi Power Bank Pro

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.

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.

  1. Charge before first use: When you buy a power bank, charge the power bank overnight before using it.
  2. 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.
  3. 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%.
  4. 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.
  5. Avoid Metal Objects: Most of the power banks have short circuit protection. But still do not put the power bank in pocket with a metal object. Better safe than sorry.
  6. 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.

Read more about power banks efficiency here.

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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.

  • Anker
  • Xiaomi
  • Mophie
  • Aukey
  • RAVPower
  • Belkin

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:

Anas Abdullah

Tech Enthusiast, Content Writer, Part-time Gamer.

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