Imagine you are stuck out in the forest, and you have 1% remaining on your mobile phone battery which is about to die.
Your chances of calling for help are very limited.
A Power Bank would be able to solve your problems.
It is a portable battery charger capable of charging many devices such as mobile phones, digital cameras, portable speakers, bluetooth headphones and much more.
A power bank contains a rechargeable battery capable of storing charge which can then be later used to charge the electronic devices mentioned above.
But, is a power bank a lithium ion battery? Lithium Ion batteries are the most commonly used rechargeable batteries used in power banks due to them having a high energy density and low discharge rate as well as being cost effective.
There are other types of rechargeable battery available which can include Lithium-Polymer (Li-Po) and Nickel-Cadmium (Ni-Cad) that are used for power banks.
The power bank
The power bank helps solve many problems, the main one being that you can charge your devices when you are not at home or office where a power outlet is located.
It gives you peace of mind when travelling far places where these power outlets become harder to find.
Let’s take a close look at the power bank.
At the heart of the power bank is the Rechargeable battery.
Without this main component the power bank would be useless.
A rechargeable battery has the ability to be charged, discharged into a load and then recharged multiple times.
Normal batteries (disposable ones) can only be used once and then have to be disposed of not making them a viable option for power banks.
Other parts of the power bank include; Charging circuit, Battery protection circuit, and Boost converter.
Charging circuit
The main purpose of the charging circuit is to provide a constant DC (direct current) or pulsed DC power to the rechargeable battery of the power bank.
Battery protection circuit
There are going to instances when you charge the power bank and forget to remove the charger, leaving it plugged in longer than required.
Lucky for us, the battery protection has the job of protecting the power bank’s battery from overcharging.
It also protects the battery from high temperatures.
Boost converter
The boost converter circuit in the power bank steps low voltages between 3.7 – 3.85 volts to the standard operating voltage of 5 volts (which is used by most electronic devices).
Why do power banks use a lithium ion battery?
Lithium ion rechargeable batteries aren’t the only batteries available when designing a power bank, however, they are the most common.
Early on, Nickel-Cadmium was the go rechargeable battery for portable equipment and wireless communication.
Lithium ions are now the preferred battery of choice, being used in almost all portable electronics and they can even be found in Electric vehicles.
The Lithium Ion battery contains electrolytes which lithium ions travel through from the negative to the positive electrode.
Compared to Nickel-Cadmium batteries, Lithium Ion batteries have a higher energy density (typically double), but there is room to increase the energy density further.
Also, the lithium ion battery has lower maintenance compared to other rechargeable batteries. There is no memory and schedule cycling is not required to prolong the life of the battery.
Below are other characteristics of the Lithium Ion Battery;
| Specific energy | 100 – 265 W.h/kg |
| Energy density | 250 – 693 W.h/L |
| Specific power | ~250 – ~ 340 W/kg |
| Charge/Discharge efficiency | 80 – 90% |
| Self – discharge rate | 0.35% – 2.5% per month |
| Nominal voltage | 3.6 / 3.7 / 3.8 / 3.85 Volts |
| Cycle life | 400 – 1200 cycles |
Lithium- ion vs Lithium polymer power bank. Which is better for a power bank?
We saw that Nickel-Cadmium batteries were used earlier on in the infancy of portable technology, and nowadays Lithium Ion batteries are the popular choice.
But, there is another rechargeable battery that is quite popular, and that is the Lithium-Polymer rechargeable battery.
Which battery is better for a power bank?
Let’s take a look at the advantages and disadvantages of both batteries which will give us a better indication of which is the better choice for a power bank.
Lithium-Ion Advantages
- High energy density
- Low self-discharge
- Low maintenance
- Speciality cells can be used for high current applications
Lithium-Ion Disadvantages
- Requires protection circuit to protect against over voltage and currents
- Can age relatively fast if not stored in cool environments
- Expensive to manufacture
- Still in evolutionary phase (lots of improvements are being made)
Lithium-Polymer Advantages
- Sleek, compact design
- Flexible
- Lightweight
- Improved safety
Lithium-Polymer disadvantages
- Lower energy density and decreased cycle count
- No standard sizes
- Higher cost-to-energy ratio
So, there are the advantages and disadvantages of both the batteries.
But, how do we know which is better to use in a power bank?
There are a couple requirements to consider of what will make an effective power bank which is ultimately determined by the battery.
- Cost
- Life cycle
- Capacity
Cost
First on the list is cost.
With anything you buy, you do not want it to cost you an arm or leg.
The same can be said when buying a power bank.
While both batteries are relatively expensive to manufacture, the cost to energy ratio of the Lithium Polymer battery is higher.
So, it is more cost effective to use a Lithium-Ion battery for a power bank as it will cost you less to get the same amount of energy as a Lithium-Polymer battery.
Life Cycle
It would be pointless if you could only use your power bank 10 times and then have to dispose of it.
The aim is to have a power bank that will last you a long time.
The life cycle of a power bank is the amount of times you can charge and discharge it before the battery wears out.
There are many factors that determine the life cycle of a battery like capacity, storage, etc.
But, generally, Lithium-Ion batteries are known to have a higher cycle count compared to their Lithium-Polymer counterparts.
Capacity
Finally on the list of requirements for an effective power bank is its capacity
The capacity of a power bank is the amount of charge it can store and thus charge other portable electronic devices.
It wouldn’t make sense if a power bank held less charge than your mobile phone.
This would mean that you would have to charge the power bank a couple of times in order to fully charge your mobile phone rendering the power bank ineffective.
The capacity of a power bank correlates directly with the energy density of the battery it uses.
The higher energy density of the battery the more power it will be able to store and therefore charge your portable electronic device multiple times.
Lithium-Ion batteries have higher energy density than Lithium-Polymer batteries.
So, you can see that the Lithium Ion meets all three requirements which determines the effectiveness of a power bank making it the better option.
Health and Safety concerns with lithium ion battery power banks?
While they have their many advantages and reasons to be used in a power bank, Lithium-Ion batteries are known for exploding and catching fire.
Due to this they have many restrictions when taking them on flights especially as carry-on luggage.
So, check with you the airline you might be flying with for what restrictions they have for power banks that use Lithium-Ion batteries.
Always store the power bank in a cool place and out of direct sunlight.
