Exploring the battery charging process

What is happening during battery charging?

In a previous article, we explored energy storage systems (ESS) and stated their advantages, disadvantages, and the important parameters to be considered when selecting energy storage systems. We also discussed batteries as one of the energy storage elements that store potential energy as a form of electrochemical and supply it as electrical energy to the applications.

Batteries play an important role in applications that require a sustainable and steady source of electrical power such as renewable energy systems, Instrumentation systems, electronic devices, and portable devices like laptops and smartphones. In this article, we will explain the different types of rechargeable batteries, how the battery charging process is controlled, and its 3 charging stages. Let us start with the rechargeable battery types.

Battery charging process

What are the most rechargeable battery types?

There are several types of rechargeable batteries that are used as an electrical power source. each type of rechargeable battery has its advantages and disadvantages. The type of applications that use batteries determines the rechargeable battery type and specifications based on the battery’s material chemical reaction. These battery types are:

1. Lead-Acid Batteries.

It has low energy density, is inexpensive, and is very suitable for applications that require high surge currents. It is used for UPS, Automotive, and renewable energy storage devices.

2. Lithium-ion batteries (Li-ion)

This type of battery has high energy density, low self-discharging over time, and a long-life cycle. It is used in laptops, smartphones, and electric vehicles. It has also several chemistries like Lithium Cobalt Oxide (LiCoO₂), Lithium Iron Phosphate (LiFePO₄), Lithium Manganese Oxide (LiMn₂O₄), and Lithium Nickel Manganese Cobalt Oxide (NMC).

3. Nickel-Cadmium Batteries (NiCd).

It is durable, and robust, can hold high discharge rates, may reduce capacity if not fully discharged, and has moderate energy density. It is used in aviation, emergency lighting, and medical devices.

4. Lithium Polymer Batteries (Li-Po). 

It is flexible and has low weight. it is used in portable electronic devices, drones, And mobile phones.

5. Nickel-Metal Hydride Batteries (NiMH).

This type has high energy density and moderate self-charging. It is used in electronic devices, cordless phones, and hybrid vehicles. automotive starter batteries.

6. Sodium-Ion Batteries.

It has a low environmental impact and is used in large-scale (ESS) energy storage systems and low-cost applications because it is still under development.

7. Solid-State Batteries.

It has a higher safety factor and low leak risk. It is very suitable for high energy density. It is used in medical devices and modern electric vehicles.

What is the battery charging process?

Battery charging is the process where the original full electrochemical potential energy of the battery is restored by reversing the chemical reactions at the anode and the cathode done through the discharging process. The charging process mainly depends on the type of battery and has to follow a certain precaution to get the full charge safely and efficiently by using the charge controller.

What is the battery charge controller?

the battery charge controller is an electronic device (like the PID controller) used in circuits that includes rechargeable batteries as an electrical power source. It manages and controls the charging voltage and current. It regulates the amount of current and voltage coming from the charging source like grid electricity or renewable sources (solar panels or wind turbines).

It also protects batteries from damage by avoiding and eliminating any hazards like temperature and pressure increases during the charging process. It protects batteries from overcharging and even exploding. It prevents the batteries from fully discharging to 0%, increasing their lifetime. Battery charge controller contains sensors to measure current voltage, temperature, and state of charge (SOC%) values

What are the battery charging stages?

There are two main stages in the battery charging process. These three stages are:

1. Constant Current stage.
2. Constant voltage stage.
3. Floating charge stage.

Constant Current stage.

In this stage, the charger controller supplies the battery with a constant current equal to 0.5 Amps multiplied by the number of the battery cells. The voltage increases from the low voltage value to the high voltage value. These two values of voltage are variable depending on the type of battery. In this stage also the charging percentage reached about 80 to 90% of the battery’s full capacity.

The current and voltage vary according to the type of battery. For Lead-Acid Batteries, the values of charging low and high voltage are from 2.23 to 2.45V/C. while in Lithium-Ion Batteries these values are about 4.2V/C. also, the charging current for lead acid batteries is about 10 to 30% of the battery capacity while in lithium-ion batteries, the current is about 0.5A/C.

Constant Voltage stage.

In this stage, the charge controller fixes the charging voltage supplied from the source at the maximum value that is reached during the constant current stage. The charging current decreased until the fully charging of the battery. This stage is also called the absorption stage where the constant voltage enables the battery to reach the full capacity without overcharging.

Floating charge stage.

This stage is the important stage during the battery charging process where the charge controller supplies batteries with a constant low value of voltage and allows the self-discharging process to maintain the battery ready for use at its full charge and at the same time avoid the overcharging of the batteries.

This stage may be called the trickle or maintenance stage. It is very suitable for lead acid batteries in applications with backup generators and UPS (Uninterrupted Power Supply). It keeps the battery healthy condition by releasing the battery stress in the long inactive time of the batteries and as a result, it increases the batteries’ life span. The below image explains the battery’s charging process.

Battery charging stages

In summary.

The battery recharging process restores the battery energy to its original energy’s full capacity. the charging process is controlled by electronic circuits known as charger controllers. The battery type is the main factor that determines the chemical reaction at the battery’s anode and cathode.

There are three stages during the recharging process. These charging stages are the constant current (CC), the constant voltage (CV), and the Floating charge stages. In a separate article, the main charging parameters, safety precautions, and temperature compensation during the charging process will be discussed.