There are so many different terms used around battery charging that we all need a charging definitions and glossary. All arranged A to Z so that you can easily scroll through.
AC Charging (Level 1 / Level 2) Charging via the vehicle’s on-board charger (OBC) using alternating current supplied by the EVSE.
- Level 1 uses a standard household socket (~1.4–1.9 kW in the US, ~2.3 kW in the UK/EU on a 230 V single-phase supply) and is typically used for overnight home charging.
- Level 2 uses a dedicated circuit, typically 7–22 kW depending on phase configuration and OBC rating, and is the standard for home wallboxes and destination charging. Both are rate-limited by the OBC rather than the battery.
Autocharge A legacy vehicle-identification method predating ISO 15118, in which the charge point identifies the vehicle by monitoring the resistance signature or communication behaviour on the Control Pilot line during connection, rather than through cryptographic authentication. Still used on some CCS installations for fleet or ad-hoc charging where Plug & Charge is unavailable.
Bank charging Split the pack in two to charge it. Thus an 800V drive pack becomes two 400V packs in parallel for charging.
Battery Preconditioning Active heating (or occasionally cooling) of the battery pack ahead of a planned DC fast-charge event, bringing cell temperature into the window where lithium plating risk is low and charge acceptance is high. Typically triggered by navigation to a mapped fast charger, using the BMS thermal management loop to raise pack temperature during the drive so the full charge curve is available on arrival rather than being taper-limited by a cold pack.
Boost charging with a CC-CV-CC-CV scheme
Calendar Ageing vs. Cycle Ageing Calendar ageing is “idle decay” driven by thermodynamics, time, and temperature while the battery is at rest. Cycle ageing is the “active-use wear” driven by ion movement and the mechanical stress of charge throughput.
Capacity Fade Refers to the loss of total energy storage (the “tank” shrinking).
Charge Curve / Charging Taper The profile of charge power (or current) against state of charge during a charging session. Fast-charging curves typically hold peak power through a low-to-mid SoC band, then taper — reducing current — as SoC rises, to manage the increasing overpotential and lithium-plating risk as the cell approaches full charge. Taper shape is cell-chemistry- and temperature-dependent, and is the primary reason manufacturer “10–80%” charge time claims don’t scale linearly to 100%.
Charging Efficiency The ratio of energy delivered to the battery versus energy drawn from the AC supply, accounting for OBC conversion losses, cable and connector resistive losses, and thermal management parasitic load during the charge event. Typically 85–95% for AC charging depending on OBC topology and load point; distinct from Round-Trip Efficiency (RTE), which additionally accounts for the discharge side.
Constant Current – Constant Voltage (CC-CV)
Constant Power – Constant Voltage (CP-CV)
C-rate The intensity of the electrical current relative to the battery’s total capacity (e.g., 1C discharges the entire battery in one hour).
DC Fast Charging (DCFC) Charging in which AC-DC conversion happens off-board at the charging station, delivering DC current directly to the battery and bypassing the vehicle’s OBC. Commonly subdivided informally into “fast” (~50 kW), “rapid” (~50–150 kW), and “ultra-rapid” or “hyper-charging” (150 kW+), though these bands aren’t formally standardised and vary by region and OEM marketing.
Demand Response (DR) Short-term services where EVs adjust their load to help the grid manage frequency and maintain reliability.
Depth of Discharge (DoD) The percentage of total capacity that is discharged during a single cycle. Frequent, high-DoD cycles are a primary stressor in cycle ageing.
Distributed Locational Marginal Pricing (DLMP) & ACOPF A methodology using AC Optimised Power Flow (ACOPF) to calculate the precise value of power at specific nodes on a distribution circuit, accounting for local congestion and voltage constraints.
Energy Arbitrage The practice of “buying” electricity when prices are low (off-peak) and “selling” it back to the grid when prices are high.
EVSE (Electric Vehicle Supply Equipment) The charging station hardware and control electronics that sit between the electricity supply and the vehicle, managing connection detection, safety interlocks, and (for AC charging) communicating the maximum available current to the vehicle’s OBC via the Control Pilot signal. The EVSE does not perform AC-DC conversion for AC charging — that happens in the vehicle’s OBC — but DC EVSE (“DC chargers”) house the power conversion stage themselves.
FERC Order 2222 A landmark US regulation (with equivalents emerging in the UK Balancing Mechanism) that allows DERs like EVs to participate directly in wholesale energy markets.
Float Charge A low, constant voltage applied to maintain a fully charged battery at 100% SoC and offset self-discharge, without driving further net charge into the cell. More common in stationary/backup lead-acid applications than EV traction packs, where BMS charge cut-off is normally used instead to avoid the sustained high-SoC dwell time associated with float charging.
GB/T The Chinese national charging connector and communication standard (GB/T 20234 for connectors, GB/T 27930 for CAN-based communication), used across the Chinese domestic EV market in place of CCS, CHAdeMO, or NACS. A newer GB/T 2025 revision has been developed with megawatt-class charging support in view, aligned with China’s fast-charging expansion targets.
Grid-to-Vehicle (G2V) Unidirectional charging in which energy flows from the grid to the vehicle only — the conventional charging mode, and the implicit counterpart to V2G. Used as a contrast term when discussing bidirectional charging capability and smart-charging scheduling (V1G).
Inrush Current The brief, high-magnitude current surge that occurs at the moment of contactor closure or charge initiation, driven by the charging equipment’s capacitive input stage or by pre-charge circuit limitations. Relevant to contactor and connector sizing, and to pulse-charging profile design where repeated current steps can produce inrush-like transients if pre-charge is not managed.
ISO 15118 & ISO 15118-20 The primary international standards for “Plug & Charge” and bidirectional data exchange. The “-20” suffix specifically enables advanced bidirectional features and high-level communication between the EV and EVSE.
Lithium Plating This is the deposition of metallic lithium on the surface of the graphite anode. This is one of the most significant degradation mechanisms.
Megawatt Charging System (MCS) A CharIN-developed connector and communication standard for charging heavy-duty vehicles (trucks, buses, off-highway and marine applications) at power levels up to ~3.75 MW, well beyond passenger-vehicle CCS limits. Uses a liquid-cooled cable and connector design and is intended to bring truck charge times into a range comparable to diesel refuelling stops.
Microgrids Localised energy systems that can operate independently using V2M for resilience.
Multistage Constant Current – Constant Voltage (MCC-CV)
OCPP (Open Charge Point Protocol) The standard for communication between the charging station and a central management system. It is essential for managing “grid-parallel” programmes, where vehicles optimise energy flow while remaining synchronised with the network.
On-Board Charger (OBC) The vehicle-side AC-DC power conversion unit that governs AC charging rate and efficiency, converting incoming AC supply to DC for the battery. OBC power rating (commonly 3.6–22 kW) sets the ceiling on AC charge speed regardless of EVSE or grid connection capacity, and is a key differentiator between trims/models offering optional higher-power AC charging.
Overcharge A critical safety issue for the large-scale application of lithium-ion batteries.
Overcharge / Overdischarge Resuming Voltage – the voltage threshold at which protection circuitry re-enables charging or discharging after tripping on an overvoltage or undervoltage fault, set with deliberate hysteresis below the overcharge trip point (or above the overdischarge trip point) so the cell doesn’t immediately re-trip the moment protection lifts.
Peak Shaving & Valley Filling Strategies to flatten the demand curve by discharging batteries during peak periods (shaving) and charging during periods of low demand (filling).
Physical Connector Standards These include NACS (SAE J3400), CCS, and CHAdeMO. While CHAdeMO pioneered bidirectional support, modern NACS and CCS standards are rapidly evolving to support high-power V2G.
Plug & Charge An automated vehicle authentication and billing method defined within ISO 15118, in which the vehicle and charge point exchange digital certificates over the charging cable to authorise and initiate charging without a card, app, or RFID token. Supersedes Autocharge and RFID-based authorisation where both vehicle and charge point support the standard.
Power Fade The loss of the battery’s ability to deliver current effectively due to increased internal resistance.
Pulse charging – charging current is pulsed, could be from minutes to many kHz.
Remaining Useful Life (RUL) A probabilistic forecast of the time remaining before a battery reaches its failure threshold (typically 80% SoH). In predictive modelling, this is often treated as a “first-passage time problem”.
Round-Trip Efficiency (RTE) The ratio of energy retrieved from the battery to the energy required to charge it. Losses occur primarily as heat due to internal chemical resistance.
SAE J1772 (Type 1) The North American and Japanese standard AC connector, defined under SAE J1772, providing single-phase AC charging up to 80 A. Physically distinct from the Type 2 (Mennekes) connector used across Europe, though both use the same Control Pilot signalling principle for communicating available current.
Smart Load Panels & Islanding Hardware required to safely disconnect a building from the distribution network during a V2H event, ensuring the site remains powered without endangering workers on the external grid.
Solid Electrolyte Interphase (SEI) Known as the “unseen thief”, this layer forms on the anode as the electrolyte decomposes. While a stable SEI protects the battery, its continuous growth consumes lithium inventory and increases resistance.
State-of-Charge (SoC) A real-time measure of the energy currently stored in the battery relative to its capacity, analogous to a fuel gauge.
State-of-Health (SoH) The ratio of the battery’s current functional capacity compared to its original, “as-manufactured” state.
State of Power (SoP) The instantaneous maximum charge or discharge power the pack can sustain within defined voltage, current, and temperature limits, for a specified duration. Distinct from SoC and SoH, SoP is the parameter that directly governs how much charge power the BMS will accept at a given moment — the underlying basis for the charge curve/taper behaviour seen at the vehicle level.
Stepped Constant Current – Constant Voltage (SCC-CV)
Stepped Fast Charge Limits The result of a limited test regime applied by the cell supplier to establish the maximum charge current for the cell.
Trickle Charge A very low, near-constant current maintenance charge applied to keep a battery topped up once at or near full charge, historically used with lead-acid batteries and simple chargers lacking full CC-CV termination logic. In modern EV/BMS contexts, largely superseded by proper charge termination and periodic top-up scheduling rather than continuous trickle current.
Type 2 (Mennekes) The standard AC connector across Europe (mandated under the EU’s Alternative Fuels Infrastructure Regulation), supporting single- and three-phase AC charging up to 43 kW, and forming the AC pins of the Combined Charging System (CCS2) connector used for DC fast charging in the same region.
UL 1741 SB/SC & UL 1741 CRD Technical standards for inverters and grid-interconnection. The UL 1741 CRD (Certification Requirement Decision) is a critical interim pathway for the certification of AC bidirectional systems as the industry moves towards the full publication of the SC standard.
V1G (Managed Charging) Unidirectional “smart” charging. V1G modulates the time and rate of the charge to avoid peak loads but lacks the hardware capability for reverse energy flow.
Variable Current Profile (VCP)
V2F (Vehicle-to-Farm) A specialised application for agricultural environments, utilising EV batteries to power irrigation systems, lighting, and machinery in remote areas.
V2G (Vehicle-to-Grid) The most complex modality, involving the export of electricity back to the distribution network. This allows for energy arbitrage and the provision of ancillary services (such as frequency regulation) to help the Distribution Network Operator (DNO) maintain grid stability.
V2H (Vehicle-to-Home) & V2B (Vehicle-to-Building) “Behind-the-meter” applications where the EV battery provides domestic or commercial backup power. These systems optimise local energy use by discharging the car to power the site during peak tariff periods or outages.
V2L (Vehicle-to-Load) The use of the vehicle’s battery to power external appliances or tools. This typically utilises the vehicle’s internal inverters and integrated AC outlets.
V2M (Vehicle-to-Microgrid) The integration of EVs into localised, often “islanded” energy systems that can operate independently of the primary grid infrastructure.
V2V (Vehicle-to-Vehicle) An emergency application enabling the sharing of charge between EVs, effectively acting as electrochemical “jumper cables” for stranded vehicles.
V2X (Vehicle-to-Everything) The overarching umbrella term for all technologies enabling energy to flow from an EV battery to an external destination, whether a device, a building, or the distribution network.
Virtual Power Plants (VPP) The cloud-based aggregation of numerous EVs and other Distributed Energy Resources (DERs) to provide services traditionally reserved for large-scale power stations.
See also: System Definitions & Glossary