The Polarium Battery Dictionary

Designed to demystify the technical jargon, our dictionary offers clear and concise definitions of key terms, components and technologies related to batteries. From the basic principles of cells to large-scale battery energy storage systems, this dictionary is a comprehensive guide for learning battery 101.

Battery cell: A cell is a basic unit of a battery, consisting of an anode (negative side), cathode (positive side) and electrolyte. The cell generates electricity through a chemical reaction between these components, causing a flow of electrons from one material to the other, which provides an electric current. A single cell has a specific voltage and capacity, which is determined by the materials used in the anode and the cathode. The cell can vary in size, shape and type of chemistry.

Battery: A battery is a collection of one or several cells connected to provide a desired voltage and capacity (that is, the amount of energy stored in the battery). The battery as a whole unit also includes additional components such as casting, terminals for connecting the device, and circuitry for management and protection. A battery is designed for a specific function or environment, where the domain will define the characteristics.

Battery chemistry: Refers to the chemical composition and reactions occurring within a battery that enables it to store and release electrical energy. Some of the most common battery chemistries are Lithium-ion, Lead-Acid and Sodium-ion. Each type of battery chemistry has its advantages and disadvantages in terms of cost, capacity, energy density, temperature sensitivity, and environmental impact.

Lithium Iron Phosphate Cells (LFP): An iron-based lithium-ion battery cell chemistry. LFP is characterized by initial low capital costs and high safety. On the downside, they have lower energy density and operating voltage and higher self-discharge.

Nickel Manganese Cobalt Cells (NMC): A nickel-based lithium-ion battery cell chemistry. NMC batteries can be optimized for energy, power or lifecycle applications depending on requirements. They provide the lowest total cost of ownership out of all lithium-ion chemistries.

Sodium-ion Cells (SiB or NiB): A sodium-based battery cell chemistry. SiB/NiB batteries are still in the development phase, but show very promising results with low capital cost, good performance and sustainable sourcing. Right now, the chemistry has a lower energy density compared to lithium-based cells.

Battery voltage: Determines the types of devices a battery can power. Each device requires a specific voltage to operate correctly. Too low a voltage may not power the device, while too high a voltage can damage it. Voltage is measured in volts (V).

Battery capacity: Refers to the amount of electric charge a battery can store and deliver to a device. It indicates how long a battery can power a device before needing to be recharged or replaced. Capacity is measured in watt-hours (Wh) or ampere-hours (Ah).

C-Rate: Defines the maximum charging and discharging current based on the capacity in ampere-hours (Ah). For example, in a battery with a capacity of 100 Ah, a C-rate of 0.5C will equal 50A max current.

Energy density: A measure of how much energy a battery can store relative to its size or weight. It’s a crucial factor in determining a battery’s performance and suitability for various applications. Batteries with higher energy densities can store more energy for their size or weight, making them desirable for many modern applications.

Energy storage solutions: A technology used to store energy for later use. There are many types of energy storage solutions, and one of the most common is battery energy storage solutions. They can be used for a wide range of applications, from small-scale electronics to large-scale grid storage.

Battery Management System (BMS): A system that controls the battery to make sure that it functions in a safe, reliable, and efficient way. The BMS includes intelligent features that allow you to analyze the battery, receive information about its state of charge and state of health, and manage it remotely to ensure optimal performance throughout the battery lifecycle.

Current Limiting Device (CLD): A protective component patented by Polarium that provides key functionality to a battery’s safety and optimizes the charging of the battery. The CLD prevents dangerous overcharging of cells, by close monitoring and limiting of charging voltage to cells irrespective of the external charging power. 

State of Charge (SoC): The remaining charge in the battery expressed as a percentage.

Depth of Discharge (DoD): Defines how much of a battery capacity you use, relative to the total capacity of the battery.

State of Health (SoH): The overall condition of the battery and its capacity in relation to its original state, BoL.

Beginning of Life (BoL): Defines the specification of a battery when new.

End of Life (BoL): Define the specification of a battery at the end of its life.

Round Trip Efficiency (RTE): Defines how much energy losses a system has. It is measured in percent, where 100 percent equals no losses.

Battery Energy Storage System (BESS): A system of battery modules, a battery management system, power conversion, and a controller that adds local computer power and connectivity. Because of its modular design, the BESS can be tailored to different needs and capacities. The system can be integrated into both larger systems and additional energy sources, which allows you to store renewable energy when produced for later usage.

Power conversion: Refers to the process of changing electric power from one form to another. This is crucial in many applications, from everyday electronics to large-scale energy storage systems. The most common forms of power conversion involve converting between alternating current (AC) and direct current (DC) or changing the voltage and current levels.

Power Conversion System (PCS): The commonly used name for bi-directional power converters used for Battery Energy Storage System (BESS). The system can both charge batteries and use energy stored in the batteries to send power back to the grid.

Energy Management System (EMS): The interface between a battery energy storage system, the user and the electric grid. Using machine learning and AI, the EMS monitors and manages the energy storage system for optimized energy consumption. By automatically forecasting system behavior and constantly following the market for ancillary services and day-ahead prices, the EMS creates an optimized schedule for energy usage.

Energy Optimization System: Consists of a Battery Energy Storage System (BESS) and an Energy Management System (EMS). The system identifies the optimal time to store and release energy and then manages your energy usage. This can reduce energy costs and create new revenue streams while maximizing the value of solar, wind and energy storage assets.

Fleet management: A system for connecting batteries and monitoring, controlling and optimizing performance across an entire battery fleet. By collecting and utilizing data, fleet management enables updates, troubleshooting and predictive and preventive management of the batteries and their firmware. This way, fleet management provides full control and visibility throughout the entire battery lifecycle.