How to determine the right power bank for you

Power Banks  are used to provide electrical power to your phones, laptops, camcorders and handheld electrical devices. They are hand held batteries you can use to charge and power your devices when traveling, off grid areas or places with epileptic power supply.

Choosing a suitable power bank

Power Banks come in various shapes and sizes. Now a very simple rule: The bigger and denser a power bank is, the more capacity it probably has. Battery capacity means how long it can power your device or how many times it can charge your device from zero to 100%. The battery capacity should be boldly written on the packaging of any power bank you intend to buy.

When shopping for a power bank, take a good look at its capacity. It is usually expressed as something mAh. For instance, power Banks can come in capacities of 5000mAh, 10000mAh, 20000mAh and so on.

Also the power rating and battery capacity of the devices you will use the power bank with, matters.

For example, let’s say someone bought you a power bank with a capacity of 10000mAh. And you will be using it to charge a Samsung note 8 phone with a battery capacity of 3300mAh. Theoretically, the power bank should be able to charge the phone from 0-100%, 10000/3300 times or 3.03 times. However because it will be around 85% efficient when new, it should charge the phone atleast 2.5times.

Buying an original power bank

When buying an original power bank, look for the originality, look at the brand name, the packaging, engravement of the brand name and logo on the body of the power bank.

The buying of fake and substandard materials cannot be overemphasized. Most power Banks are made with lithium technology. These lithium batteries are usually purchased brand new in standard sizes from merchants and then used to build power Banks of various capacities. 

Some power bank makers can cut corners by buying and using used lithium batteries to build power Banks for sale.

How long your power bank can last

How long your power bank will last depends on the number of charge and discharge cycles it can afford before it becomes unusable. It depends on the type and quality of the lithium batteries.

Power banks made with lithium polymer batteries should at least have a charge-discharge cycle of around 200 times,

Those made of lithium ion at least 300times and those made of lithium phosphate batteries about 1000 times or more. This means a good power bank can last you for more than a year if properly used. Some power Banks can last for 2 to even 4 years.

Care for your power bank

Most power Banks will not last if misused.

When you purchase a new power bank you may be told by the manufacturers to charge it for a certain number of hours before use. Heed this counsel for your batteries to last longer.

Don’t let it drop or fall on the floor, some internal components may become broken or detached which may render it unusable.

Always use the original charger that came with the power bank to charge it.

Don’t let water or other liquids find their way into your power bank.

Don’t put your power bank in a hot room or under direct sunlight.

Don’t charge your power bank or use your power bank to power/charge a device in a hot room.

Do not over discharge your power bank, thankfully most power Banks come with a screen display to monitor the amount of battery power remaining. They are also equipped with circuit boards that prevent over charging and over discharging.

How to connect batteries in series and parallel. Simply explained .

Battery cells connected in series

Batteries connected in series

A series connection of batteries is achieved when the negative terminal of one battery  cell is connected to the positive terminal of another battery cell. 2 or more battery cells can be connected this way. An example of application of series connection of batteries is in the use of a touch light. Typically 2 batteries are connected in series for the touch light to come on.

In a series connection of batteries, voltage increases while current stays constant.

For example let’s say 2 battery cells are rated 1.5 V and 1A each and the cells are connected in series. Then the combined voltage for the series connection  becomes 1.5V + 1.5V = 3V but the current remains 1A.

Using the previous cell ratings, an electrical appliance that needs 6 volts to come on will require 4 battery cell connection in series

Battery cells connected in parallel.

batteries connected in parallel

A parallel connection of batteries is achieved when the positive terminal of one battery cell is connected to the positive terminal of another battery cell. The same is done to the negative terminals of the battery cells.

In a parallel battery connection, voltage stays constant but current increases.

For example let’s say 2 battery cells are rated 1.5V and 1A each. If the batteries are connected in parallel then their combined ratings are 1.5V and (1A +1A) = 2A

Application of series and parallel connection of battery cells

A very good knowledge of series and parallel connection of battery cells enables the development of battery packs with with different voltage ratings and capacities.

Types of Lithium Batteries

There are many types of lithium batteries. The 3 most common types of commercially available ones will be briefly discussed. They are;

Lithium ion (Li-ion)

Lithium Polymer (RC Lipo)

Lithium Iron Phosphate (Life PO4)

Lithium ion (Li-ion) batteries

Lithium ion 18650 batteries

These are the most common types used in consumer electronics like laptops, cell phones, power tools etc. They have the highest energy to weight ratios. These batteries are relatively safe, they won’t just burst into fire. They have  long cycle lives. The shortest is about 300 discharge circles, and can reach as high as 1000 discharge circles. The most common workable form is the 18650 cylindrical cell ( 18mm dia. & 65mm height). They have nominal voltage of around 3.7V and a discharge-charge voltage range of 2.5V- 4.2V.

Lithium Polymer (RC Lipo) Batteries

lithium polymer battery

These batteries can provide high discharge rates for long periods of time. They are used for equipment that require high discharge rates such as Remote control led drones, helicopters, cars, planes etc. These batteries are very cheap, cheaper than a typical lithium ion and life PO4 battery. They have very short cycle lives, about 200 recharge discharge cycles. They have a lower discharge – charge range of about 3V – 3.7V. They are very volatile and can easily burst into flames if not carefully handled.

Lithium Iron Phosphate (LifePO4)

lithium ion Life PO4 battery

LifePO4 battery cells are heavier and less energy dense than most lithium ion cells. 

These batteries have the longest cycle life of all the common lithium battery cell types.

They have a nominal voltage of about 3.2 V per cell and discharge- charge voltage of 2.5V- 3.65V. The Best applications for LifePO4 cells are projects that require long cycle lives and high safety.

General information in Lithium batteries

Lithium battery cells when fully charged can read up to 4.2V and at its discharged state reads 2.5V. Lithium battery cells discharged below 2.5 V will cause irreparable damage to the cell. This is why Lithium batteries are fitted with a battery management system, BMS. The main function of BMS is to ensure that the battery is properly charged as well as to prevent overcharging and over discharging.

Forms of Lithium Batteries

Lithium batteries have been available since the 1970s. Technological advances in Lithium battery research have made it the most sought after now. Lithium batteries have a high energy to weight ratio, over 1000 discharge cycles and fast recharging. These batteries are used in mobile phones, security gadgets, drones, electric cars and so on.

Composition of a typical lithium battery cell.

composition of a lithium battery cell

A lithium battery is composed of 4 parts namely;

Cathode: (+ terminal). It is a lithium compound mixed with other materials.

Anode: (+negative terminal). It is a graphite material.

Electrolyte:  An organic compound containing lithium salts to transfer lithium ions.

Porous separator:  Allows lithium ions to pass through itself but separating the cathode and anode.

Form of Lithium batteries

Pouch lithium cell

Pouch: These forms  of lithium batteries look like thin foil bags. They have two terminals at an edge of the porch. They are lightweight and cheap to produce. They are used to power cell phones and some types of  laptops.

Prismatic lithium ion cell

Prismatic: these are similar to pouch in form but more robust. The battery cells are placed in rigid rectangular cases. They have threaded terminals which makes building of larger batteries easier. They are used in high energy storage devices such as electric vehicles and home use.

Cylindrical lithium ion cell

Cylindrical: These forms of lithium batteries look like the AA batteries we use in our touch lights and remote controls. However the cylindrical lithium battery form is much larger than a typical AA battery in size. Unlike pouch and prismatic forms of lithium batteries, the sizes of cylindrical lithium batteries are standardized. The most commonly used cylindrical battery size is the 18650 cell. The 18650 cell means that the Lithium battery cell is 18mm in diameter and 65 mm long. There are other standard sizes too like the 14500 cell ( 14mm dia & 50mm length) and the 26650 cell( 26mm dia & 65 mm length). Cylindrical lithium battery cells are used in laptops, power banks, electric cars, solar system and so on.