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Power Banks 101: All You Need to Know

Eloisa Latorre

Posted on August 27 2018

WHAT IS A POWER BANK?

 
A power bank is a type of portable battery charger use to power up your electronic gadgets when you are on the move without the need for a wall outlet. Power banks come in a variety of sizes to suit different needs. You can find pocket size power bank chargers – also known as a mobile battery, external battery, or battery packs to name a few, which can recharge small devices such as smartphones. Bigger sizes are available as well in order to juice up bigger electronic devices such as laptops and tablets. 

There are 2 major types of power banks:
  1. Solar charged power banks: these use photovoltaic panels (solar panels) to charge the battery when the panels receive sunlight
  2. Universal power banks: these are the most common. They come in many different format and sizes and have USB ports
 

HOW DO POWER BANK CHARGERS WORK?

The basics of power banks are that they supply power to your devices from its built-in battery via a USB port. However, there is a little bit more to that simple statement:
A power bank is energy stored the same way as in a battery. It has a sophisticated circuit to be charged and to charge other devices by using input and output ports. The main body of a power bank charger comprises input and output ports, the charging circuit, the battery, the discharging circuit and battery indicators. The input port is the connection to the charger and the output port is where the devices you want to charge connect to the power bank. The charging circuit recharges the power bank from a charger and regulates the voltage that will supply to the battery. The battery is where the energy charged is storage. The discharging circuit withdraws the energy from the battery, and finally, the battery indicators are visual indicators to monitor the battery level at all times.
 
SUAOKI How power banks work
source: SUAOKI
 

WHAT ARE POWER BANKS MADE OF?

Most power banks use either Li-Ion or Li-Polymer batteries, as these are the most common rechargeable cell types found in power banks.  Li-Ion (Lithium-Ion) cells are cheaper than Li-Polymer (Lithium-Polymer) cells. 

The pros of Lithium-Ion batteries are its size and weight, as they are smaller and lighter, they have a high energy density, low maintenance, and have relatively low self-discharge compared to other batteries. Moreover, this type of battery work in a wider temperature range. Despite the pros, it also has some cons. Li-Ion batteries are fragile and require a protection circuit in order to maintain safe operation.

Lithium-Polymer batteries are normally used when the battery needs to have a particular shape that isn’t rectangular or cylindrical as they replace the liquid electrolyte from the Li-Ion by a polymer. Some of the pros of Li-Polymer batteries is that they can have a very low profile, they are more resistant to overcharge and they are light. The cons are that these are more expensive to manufacture and have a lower energy density compared to Li-Ion, which results in a decreased cycle count.
 
 

CAN I CHARGE MY LAPTOP WITH ANY POWER BANK?

No. Not every power bank can charge a laptop. In order to know whether your power bank is suitable to power up your laptop, you have to check out the voltage output. Most power banks in the market have a voltage output of 5V or less, which is ideal to juice up small electric devices such as your smartphone. However, laptops and other larger devices require a higher voltage output (around 16V to 20V). You can check the voltage required by your electric devices by looking at the AC adapter.
 
 
SUAOKI Power banks airplane
source: best-wallpaper
 
 

CAN YOU BRING A POWER BANK ON A PLANE?

Yes, but. Carrying a device with power can raise a few safety concerns, which is why you can travel with a power bank, although there are some rules and limitations by the Federal Aviation Administration that you are about to discover.

If your power bank uses Li-Ion batteries, it “must be carried in your carry-on baggage only”. Why? Because batteries contain oxidizer and fuel and it exists a minimum chance that they react and explode. If this occurs in the cabin, the damage can be easily controlled by the cabin crew. However, if this occurs in the cargo hold, there are higher chances that other substances in the cargo react with the explosion creating a bigger problem to the airplane.

Secondly, certain power banks with very high capacity cannot fly at all. The Federal Aviation Administration says that “Lithium-ion (rechargeable) batteries are limited to a rating of 100-watt-hours (Wh) per battery”, and with prior airline approval “passengers may also carry up to 2 spare larger Li-Ion batteries (101-160Wh)”.
 
 

HOW CAN YOU CALCULATE Wh?

Now that you know that Lithium-Ion batteries rated above 100Wh per battery are not allowed on planes, you should learn how to calculate the Wh (Watt-hours). Luckily for you, you only need a simple formula and your phone’s calculator.
 
(mAh/1000) x V = Wh

(mAh (milliamp hours) / 1000) x Nominal Voltage (for a Li-Ion is typically 3.7V) = Watt Hours
Take a 20,000mAh Power Bank

(20000mAh/1000) x 3.7V = 74Wh  As it is under 100Wh, you can take it with you on your carry-ons
 

 

GLOSSARY

mAh: stands for mill amperes per hour. This unit is commonly used to describe the capacity of a battery. It is based on how long a battery will last when power is drawn constantly. For example, a 10,000 mAh power bank will power up a device that requires 100 mAh for 10 hours.

Amps: stands for ampere, which is a unit of current. The amps describe the average current that goes through the circuit of your power bank.

Wh: stands for Watts per hour. It is a measure of electric energy

V: short for Voltage.

Efficiency: while power is transferred from the power bank to your device, there is some loss, this is why power banks cannot transfer 100% of their capacity. You can expect your power bank to transfer around 80%-90% of the total of its capacity.

USB port: stands for Universal Serial Bus port. USB ports allow communicating 2 devices in order to transfer data and or supply power from one to the other. There are different types of USB ports:
  • USB-A: also known as the standard USB. This kind of USB are suitable to use with laptop, computers, wall chargers, and many other devices
  • Micro-USB: smaller than USB-A. Most Android smartphones use this type of USB connector. Other devices such as cameras, or e-books also use Micro-USB
  • USB-C: it is widely known as Type-C. It is a relatively new USB connector with a reversible head which is spreading among the largest companies and it transfers the power faster.
 

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