A plain-English reference to the terms used across home battery storage systems — from cell chemistry and cycle life to grid codes and communication protocols. Written for homeowners, installers and specifiers comparing residential energy storage options.
Battery basics
kWh (kilowatt-hour)
A unit of energy. In home storage it describes how much electricity a battery can hold. A 10 kWh battery can run a 1 kW load for about ten hours, ignoring efficiency losses. Usable energy is always lower than nameplate capacity because the battery does not discharge to zero (see depth of discharge).
kW (kilowatt) and kVA
A unit of power — how fast energy flows. A battery’s kW rating limits how much load it can carry at one moment. Capacity (kWh) and power (kW) are different things: a system can be large in energy yet small in power.
LiFePO4 / LFP (lithium iron phosphate)
A lithium-ion chemistry using an iron-phosphate cathode. It is the dominant chemistry in home storage because it is thermally stable, has a long cycle life and holds up well under daily deep discharge. Its energy density is lower than nickel-based chemistries, which is why LFP home batteries are physically larger for the same capacity.
BMS (battery management system)
The electronics that monitor and protect a battery. A BMS measures cell voltage and temperature, balances cells, prevents over-charge and over-discharge, and reports state of charge to the inverter. Layered protection schemes are described by the number of separate safety functions they implement.
Cell, module, pack
The three levels of battery construction. A cell is the smallest unit that stores energy. Cells are grouped into a module. Modules are assembled into a pack — the finished enclosure that is installed in a home.
Cell balancing (passive and active)
The process of equalising charge across cells so the weakest cell does not limit the whole pack. Passive balancing dissipates excess energy as heat. Active balancing moves energy between cells and is more efficient but more complex.
DoD (depth of discharge)
The percentage of capacity that is actually used on a cycle. A battery discharged to 90% DoD delivers more usable energy than one limited to 80%, but at some cost in cycle life. Manufacturers publish the DoD at which their cycle-life figure is measured.
SoC (state of charge)
How full the battery is, expressed as a percentage. It is the battery equivalent of a fuel gauge.
C-rate
The speed at which a battery is charged or discharged relative to its capacity. A 1C rate on a 10 kWh battery means 10 kW. Home batteries usually operate well below 1C, which reduces stress and heat.
Cycle life
The number of charge–discharge cycles a battery completes before its capacity falls to a stated percentage of the original — typically 80% or 60%. Cycle life is always quoted at a specified temperature and depth of discharge, so figures measured under different conditions are not directly comparable.
Round-trip efficiency
The share of energy put into a battery that can be taken back out, covering losses in conversion and storage. Expressed as a percentage; the remainder is lost as heat.
Calendar ageing
Capacity loss that occurs over time regardless of how often the battery cycles. It is driven mainly by temperature and by the average state of charge the battery is held at.
Thermal runaway
A self-sustaining temperature rise inside a battery cell. It is the central safety concern for lithium batteries, and the reason LFP chemistry, cell-level testing and enclosure design matter. Standards such as UL 9540 and IEC 62619 exist largely to test resistance to it.
System and installation
Hybrid inverter
An inverter that manages solar panels, a battery and the grid through one unit. It can charge the battery from solar, discharge it to the house, and export or import from the grid.
AC-coupled vs DC-coupled
How a battery connects to a solar system. DC-coupled means the battery shares the solar array’s DC bus, which avoids one conversion step. AC-coupled means the battery connects on the AC side through its own inverter, which makes it easier to add storage to an existing solar installation.
MPPT (maximum power point tracking)
The control that continuously adjusts a solar array’s operating voltage so it delivers its maximum available power under changing light and temperature.
Off-grid, on-grid and grid-tied
On-grid systems operate alongside a utility supply. Off-grid systems operate with no utility connection and must be sized for the worst-case period without sun. Most home batteries are on-grid with backup capability.
Backup power and transfer time
The ability to keep selected circuits running during a grid outage. Transfer time is the gap between the grid failing and the battery taking over; sensitive electronics need a short transfer time.
Peak shaving
Discharging the battery during periods when electricity is most expensive, to reduce the peak power drawn from the grid. On tariffs with a demand charge, shaving the peak lowers the bill directly.
Time-of-use (TOU) arbitrage
Charging the battery when off-peak electricity is cheap and discharging it during peak-rate hours. The value depends on the spread between the two rates and on how many cycles the battery performs.
Self-consumption
Using solar generation on site instead of exporting it. A battery raises the self-consumption rate by storing midday surplus for evening use, when household demand peaks.
VPP (virtual power plant)
A network of home batteries coordinated by a utility or aggregator to act as one large resource — for example, discharging together during a system-wide peak. Participation requires a battery with suitable communications and a supporting tariff.
IP rating
An ingress-protection rating for enclosures, written as IP followed by two digits. The first digit covers solids, the second covers water. An IP54 battery is protected against dust ingress and splashing water, which allows installation in a garage or sheltered outdoor position rather than a dry indoor room only.
Form factors
Stackable battery
A modular design where identical modules stack vertically, so capacity is chosen by the number of modules rather than by buying a different product. A stack can be sized to the household at installation and extended later as demand grows.
Wall-mounted battery
A slim enclosure fixed to a wall. It saves floor area, which suits garages and utility rooms where space is tight, and keeps the battery clear of standing water.
Floor-mounted battery
A freestanding enclosure that rests on the floor. It supports larger capacities and heavier modules than a wall fixing, and is often used where a wall is not structurally suitable.
Rack-mount battery
A battery built to standard rack dimensions, installed in a cabinet. Common where several units are combined for higher capacity.
Parallel expansion
Connecting additional battery units to an existing system to raise total capacity and power. The number of units that can be paralleled is limited by the inverter and by the battery’s own control electronics.
Communications and compatibility
CAN bus
A robust two-wire communications standard widely used between batteries and inverters. It is the default choice for closed-loop battery communication.
RS485 and RS232
Serial communications standards, also used for battery-to-inverter links and for monitoring. RS485 supports longer cable runs and multiple devices on the same bus.
Modbus
An open protocol commonly carried over RS485 or TCP that defines how registers are read and written. It is widely used for monitoring and for integration with home energy management systems.
Closed-loop communication
A setup where the battery continuously reports its state to the inverter and the inverter adjusts its behaviour in response. It is more accurate than open-loop operation, where the inverter infers battery state from voltage alone.
Inverter compatibility
The practical question of whether a given battery will work with a given inverter. It depends on matching voltage windows, communication protocol and the inverter’s own approved battery list.
Standards and certification
UL 9540
The North American safety standard for energy storage systems, covering the complete system rather than the cells alone.
UL 1973
The North American safety standard for batteries used in stationary applications. It covers cells, modules and packs, including electrical, mechanical and thermal requirements.
IEC 62619
The international safety standard for secondary lithium cells and batteries used in industrial applications, including stationary energy storage.
UN 38.3
The transport-test standard for lithium batteries. Every lithium battery shipment must have a UN 38.3 test summary, and carriers require it before accepting air, sea or rail freight.
MSDS / SDS
The material safety data sheet listing a product’s chemical composition, hazards and handling requirements. Required alongside UN 38.3 for shipping lithium batteries.
CE marking
The declaration that a product meets the applicable European Union health, safety and environmental requirements. It is a manufacturer’s declaration, supported by test documentation.
CB Scheme
An international mutual-recognition arrangement for electrical product safety test reports. A CB test report allows national certifications to be obtained in member countries with reduced repeat testing.
PSE mark
The Japanese electrical safety marking required for regulated products sold in Japan.
Customisation terms
Custom capacity and voltage
Building a battery to a specified energy capacity and nominal voltage rather than selecting a catalogue item. It is used where a household’s load profile, backup duration or available space does not match a standard model.
Custom enclosure
A housing built to a specified size, shape or finish so the battery fits a particular installation position or matches a room’s appearance.
OEM and ODM
OEM means a manufacturer builds a product to a customer’s specification and brand. ODM means the manufacturer also designs it. Both describe who owns the design versus who owns the brand.
Branding and private label
Applying a customer’s own brand to a battery — enclosure graphics, display interface, packaging and documentation — so it ships as that brand’s product.
Comparing systems
Two systems with the same kWh figure are not equivalent. When comparing home batteries, check the depth of discharge at which capacity is quoted, the cycle life and the temperature it was measured at, whether the inverter supports closed-loop communication with that battery, the IP rating against the intended install location, and the certifications held for the market the system will be installed in.
For sizing guidance see how to size a home battery. For installation requirements see home battery installation location. For standards held across the range see home battery certifications.