SoC — State of Charge
The State of Charge (SoC) indicates the current charge level of a cell or battery pack as a percentage of nominal capacity. SoC 100 % means fully charged, 0 % fully discharged. The BMS typically calculates SoC via coulomb counting (current-time integration), corrected at open-circuit voltage points. With LiFePO4 this is demanding because the discharge curve is nearly flat over wide ranges.
SoH — State of Health
The State of Health (SoH) describes the ageing condition of a battery relative to its new state. It is derived from the measured remaining capacity and the increased internal resistance. An SoH of 80 % is the industry-standard end-of-life threshold (EOL) — the pack then delivers only four-fifths of its original capacity. SoH is the basis for condition-based maintenance planning and remaining-life forecasts.
DoD — Depth of Discharge
The Depth of Discharge (DoD) indicates what fraction of nominal capacity is drawn in one cycle. A DoD of 80 % means the battery is discharged from 100 % to 20 % SoC. Deeper DoD values reduce cycle life significantly, while shallower discharge depths extend service life considerably. In AGV practice a DoD of 70–80 % is often chosen as a compromise between capacity utilisation and service life.
C-Rate
The C-rate normalises the charge or discharge current to the nominal capacity of the battery. For a 100 Ah pack, 1C equals 100 A; 2C equals 200 A. Higher C-rates generate more heat and stress the cells more, reducing service life. For continuous charge and discharge applications the recommended C-rate is typically 0.5C to 1C; short-term peaks can be significantly higher depending on cell technology.
BMS — Battery Management System
The Battery Management System (BMS) is the protection and monitoring electronics inside the battery pack. It measures cell voltages, currents and temperatures, balances cell imbalances, limits charge and discharge current, and protects against over- and undervoltage as well as short circuit. In industrial operation the BMS communicates via fieldbuses such as CAN bus or SMBus with the higher-level machine controller and delivers SoC, SoH and fault codes in real time.
LiFePO4 — Lithium Iron Phosphate
LiFePO4 (lithium iron phosphate, LFP) is a lithium-ion cell chemistry with particularly high thermal stability and long cycle life. The nominal voltage is approximately 3.2 V per cell, the permissible voltage window roughly 2.5 V to 3.65 V. LFP cells have lower energy density than Li-NMC but are significantly more thermally stable and are the preferred choice for applications with many full cycles — such as AGV, FTS or stationary storage.
Li-NMC — Lithium Nickel Manganese Cobalt
Li-NMC (lithium nickel manganese cobalt oxide) is a lithium-ion cell chemistry with high gravimetric and volumetric energy density. The nominal voltage is approximately 3.6–3.7 V per cell, the voltage window roughly 3.0 V to 4.2 V. Li-NMC suits weight- or space-critical applications, but has lower thermal stability than LFP and places higher demands on the thermal management of the pack.
LTO — Lithium Titanate
LTO (lithium titanate) is a lithium-ion cell chemistry in which the anode material consists of lithium titanate rather than graphite. LTO cells are characterised by extremely fast charging capability (5C–10C are typical), very high cycle life and excellent cold performance. However, energy density is significantly lower than for LFP or Li-NMC, which limits LTO to applications with the highest demands on fast charging and service life.
Cell Balancing
Cell balancing refers to the BMS measure of compensating voltage differences between series-connected cells. In passive balancing the highest cell is discharged via a bleed resistor until the others catch up. In active balancing charge is redistributed from the fullest to the emptiest cell — lower losses, but more complex circuitry. Without balancing the cells drift further apart with every cycle, progressively reducing the total pack capacity.
UN 38.3
UN 38.3 is the UN transport test standard for lithium cells and batteries. It requires a series of tests — including altitude simulation, thermal cycling, vibration, shock, external short circuit and overcharge — before lithium batteries may be transported as dangerous goods by air, sea or road. The manufacturer must provide a test summary; without it transport is not permitted.
IEC 62619
IEC 62619 is the international safety standard for secondary lithium cells and batteries for use in industrial applications. It defines safety requirements for design, manufacture and testing, and is a key document for the CE conformity of industrial batteries. The standard supplements the product-specific tests of UN 38.3 with systemic safety requirements for BMS, cell protection and abuse resistance.
CE Marking
The CE marking indicates that a product complies with applicable EU directives. For industrial battery packs the Low Voltage Directive (LVD, 2014/35/EU), the EMC Directive (2014/30/EU) and, where integrated into machinery, the Machinery Directive (2006/42/EC) are relevant depending on the application. The declaration of conformity is held by the manufacturer; without it the product may not be placed on the EEA market.
IP Protection Rating (IEC 60529)
The IP protection rating (Ingress Protection) per IEC 60529 classifies the protection of an enclosure against solid foreign bodies and water. The first digit describes solid particle protection (0–6), the second moisture protection (0–9K). IP54 means dust protection and splash-water protection; IP67 means dust-tight and protected against temporary immersion. For AGV and industrial trucks operating in wet warehouses or outdoors, IP65 or higher is frequently required.
Cycle Life
Cycle life indicates how many full charge-discharge cycles a battery can withstand at a defined DoD and defined conditions before its capacity falls to 80 % of the new value (EOL criterion). LFP cells achieve several thousand cycles under favourable conditions; Li-NMC typically some hundreds to over a thousand. High temperatures, deep DoD values and high C-rates shorten service life.
Energy Density
Energy density describes the storable energy relative to mass (gravimetric, Wh/kg) or volume (volumetric, Wh/L). Li-NMC achieves higher gravimetric values than LFP; LFP has advantages in safety and service life. For AGV applications volumetric energy density is often decisive because the installation space in the vehicle underfloor is limited.
Nominal Voltage
Nominal voltage is the nominal operating voltage of a cell or pack under standard conditions. It lies between the charge and the discharge cut-off voltage depending on cell chemistry. For LiFePO4 the nominal voltage is approximately 3.2 V per cell; a 48 V pack therefore consists of 15 LFP cells in series. The actual terminal voltage deviates from the nominal voltage depending on state of charge and load conditions.
Nominal Capacity
Nominal capacity (Ah) is the amount of electrical charge a freshly charged battery can deliver under defined discharge conditions (temperature, C-rate, cut-off voltage). The usable capacity in operation is below the nominal capacity due to the chosen SoC range (DoD) as well as ageing and temperature penalties. Manufacturers typically specify nominal capacity at 0.2C and 25 °C.
CAN Bus
CAN bus (Controller Area Network) is a serial fieldbus protocol originally developed for automotive electronics and today widely used in mobile working machines, AGV and industrial battery packs. The BMS communicates SoC, SoH, cell voltages, temperatures and fault codes to the higher-level controller via CAN bus. Common profiles are CANopen (including CiA battery profiles) and J1939 for commercial vehicles.
SMBus
SMBus (System Management Bus) is a digital communication protocol based on I²C, developed for connecting smart battery systems (SBS) to a host. It defines a standardised register set for capacity, voltage, current, temperature and fault status. SMBus is frequently used in smaller battery packs and portable devices; for mobile industrial machines CAN bus is the more common choice.
Lithium Plating
Lithium plating refers to the unwanted deposition of metallic lithium on the graphite anode, which occurs when the charge current is too high or the cell temperature is too low (below approximately 0 °C). The deposited lithium forms dendrites that can penetrate the separator material and cause an internal short circuit. Lithium plating is one of the main causes of irreversible capacity loss and thermal runaway.
Thermal Runaway
Thermal runaway is a self-reinforcing exothermic reaction in a lithium cell: heat accelerates chemical decomposition reactions that generate further heat — through to the uncontrolled release of energy, gases and in extreme cases fire. Triggers include mechanical damage, overcharging, external heat sources or internal short circuit. Thermal management and a well-designed protection circuit in the BMS are the primary countermeasures.
Discharge and Charge Cut-Off Voltage
The discharge cut-off voltage is the lower voltage limit at which the BMS terminates or disconnects the discharge process to prevent irreversible cell damage. The charge cut-off voltage is the upper limit to which charging proceeds. Both limits are cell-type specific: for LFP typically 2.5 V (discharge) and 3.65 V (charge) per cell. Precise setting of these limits in the BMS has a direct impact on pack capacity, service life and safety.