What does the state of charge of a lithium-ion battery mean?

Are you looking to know how much energy is left after the battery is used. Well, the amount of energy that has been used yet is known as the state of charge of a lithium-ion battery. Once your lithium-ion battery is fully charged and backing up the appliances or machinery, how much energy is left? 

The technical term used to tell the amount of energy left in the lithium-ion battery is a state of charge.

What is the state of charge of a lithium-ion battery?

The amount of energy left in the lithium-ion battery would be the state of charge. It will let you know how long the lithium-ion battery will back up your energy-consuming appliance, machinery, and other device. The state of charge of a lithium-ion battery would be expressed as % of energy left in the battery. If you can see 95%, you still have hours of backup before you run out of energy.

On the contrary, if you have seen a 10% state of charge, it is already time to recharge your lithium-ion battery before running out of energy backup. So generally, the state of charge or SOC is the reading that tells you about the remaining amount of energy in the lithium-ion battery. It will let you know whether you can keep using its energy or if it is time to plug in the charge before everything goes blank. 

For how long the lithium-ion battery can provide the backup?

You have been consuming energy stored in the lithium-ion battery, but how long can the battery give you a backup? Once you know the state of charge of the lithium-ion battery, you will be able to get the answer to this question. 

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If it is full, that means you are going to get the backup for several hours. If the state of charge is at a dead level, you will run out of backup any time soon.

You might have got an idea here how you can tell that for how long the lithium-ion battery can make your machinery or appliances keep operating depends on its state of charge. 

If you have already unplugged the charger from the lithium-ion battery, then its energy will keep decreasing as consumed by the devices, appliances, or machinery connected to it.

Long story short, the state of charge of a lithium-ion battery will let you know for how long it can provide you with a backup or if it is already time to recharge it before you run out of electricity.

What are the prediction methods for the state of charge of lithium-ion batteries?

How can you predict the state of charge of lithium-ion batteries so you would know that they are still good to go or it is time to recharge them? Following are the 3 common prediction methods for the state of charge of lithium-ion batteries:

Discharge Test Method

One of the most common methods to get a hint of the state of charge of the lithium-ion battery is through the discharge test method. It is one of the easiest ways of knowing the state of charge because you will have to just charge and discharge the battery repeatedly at a certain charge and discharge rate. 

Coulomb Counting Method

Performing this method is quite easy as you just have to calculate the remaining energy in the lithium-ion battery by accumulating the amount of charge transferred in and out. 

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Kalman Filter Method

It is kind of a mathematical way of knowing the state of charge of the lithium-ion battery. In this, you will have to work on two terms: predict and update. Predict the time that the battery provided the backup in the past. You keep updating the data for how long the battery still provides energy backup. In this, you have to compare the lithium-ion battery's previous and current time step phases.

Battery State of Health vs. State of Charge

You might get confused about the difference between state of health and state of charge. Both terms are related to lithium-ion batteries' energy storage, but they have different meanings. 

So, let's discuss the differences between these two technical terms that have you confused:

State of Health

State of health is a technical term that you must know about the lithium-ion battery before you buy it. The state of health means the storage capacity of the battery. Well, you must know the energy capacity before you buy the battery, and it will let you know for how long the battery will provide you with a back.

Different sizes of lithium-ion batteries are available in the market with different states of health, which means various energy storage capacity details. If you are buying a brand new battery, it has a 100% state of health, but if you are buying an already used battery, then the state of health won't be 100%.

State of Charge

The remaining amount of energy in the lithium-ion battery is known as its state of charge. If you have unplugged the charger and are now using the battery energy, then you can check its state of charge after a few hours to know for how long it will keep running. 

If the state of charge is already dead, the battery has no energy left. Plus, you get to know the state of charge of your lithium-ion battery in percentage. It gets easier to read the state of charge and know how long you have the backup. 

There is a difference between the state of health and the state of charge of a lithium-ion battery. So, you don't have to confuse and mix these terms because they have different meanings, but it is all about energy capacity. 

Final Words:

You ask about the state of health before you purchase of a lithium-ion battery. It is very important if you want your lithium-ion battery to last long. You can use the methods mentioned above to know the state of charge of your lithium-ion batteries.