Core battery terminology
Cell – Basic electrochemical unit converting chemical energy into electrical energy through oxidation and reduction reactions.
Module – A group of cells connected in series or parallel and placed in a mechanical frame with sensors and protection.
Rack – Structural frame containing several modules, busbars, monitoring circuits, and fuse.
Battery pack – Complete battery assembly including modules, cabling, sensors, and thermal interfaces.
Battery energy storage system (BESS) – A fully integrated system consisting of battery packs, power electronics, control units, and auxiliary systems for charging and discharging electrical energy.
Anode – Negative electrode where lithium ions are released during discharge.
Cathode – Positive electrode where lithium ions are inserted during discharge.
Electrolyte – Ion-conducting medium allowing transport of lithium ions between electrodes.
Separator – Microporous membrane keeping electrodes apart while enabling ionic flow.
State of charge (SoC) – Proportion of stored energy in a cell or system compared to its total capacity.
Depth of discharge (DoD) – Percentage of total capacity removed during a cycle.
State of health (SoH) – Indicator of remaining performance compared to the initial state, based on capacity and internal resistance
C-Rate – Charge or discharge rate relative to nominal capacity (1C= full charge/discharge in one hour).
Cycle life – Number of complete charge-discharge cycles before usable capacity drops below a defined limit.
Calendar life – Time-based aging of a cell independent of cycle count, mainly affected by temperature and voltage.
Throughput – Total energy processed over lifetime, measured in megawatt-hours.
Internal resistance (IR) – Resistance inside a cell determining power capability and heat generation.
Thermal management system (TMS) – Subsystem controlling battery temperature through liquid or air cooling and heating.
Battery management system (BMS) – Electronic unit that monitors cell voltages, currents, and temperatures, balancing charge and providing protection.
Balancing – Process of equalising voltages across cells to maintain uniform state of charge.
Self-discharge – Natural energy loss when a battery is idle due to internal chemical reactions.
Energy density – Amount of energy stored per kilogram or per litre of battery material.
Power density – Amount of power delivered per kilogram or per litre.
Nominal voltage – Average working voltage of a cell or module used for design and rating.
Voltage window – Safe operating range between minimum and maximum cell voltage.
Current limit – Maximum allowable current during charge or discharge to avoid degradation.
Charge profile – Pattern of voltage and current during the charging process.
Discharge profile – Pattern of current draw and voltage drop during discharge.
SOC window – Software-defined upper and lower SoC limits used to reduce aging.
Nominal capacity – Rated energy content available under standard conditions.
Usable capacity – Practical capacity available within defined voltage and temperature limits.
Charge acceptance – Ability of a cell to accept charge at a given current without exceeding limits.
Overcharge – Condition when voltage exceeds maximum specification, causing accelerated degradation.
Overdischarge – Condition when voltage falls below safe minimum, risking irreversible damage.
Thermal gradient – Difference in temperature between areas of a cell or module affecting performance uniformity.
Impedance growth – Increase of internal resistance over time due to aging and side reactions.
Passivation layer (SEI) – Protective film formed on the anode surface stabilising lithium-ion reactions.
Formation process – Initial controlled charge cycles during cell manufacturing to build the SEI layer.
Gas generation – Release of gases during side reactions, typically at high voltage or temperature.
