Battery Glossary
Plain-language definitions of essential battery, charging, performance and BMS terminology.
Core electrical terms
Ah — Amp-hour
A unit of electric charge. Pair it with voltage to estimate energy. See Ah vs Wh.
Wh — Watt-hour
A unit of energy equal to one watt delivered for one hour.
C-rate
Current normalized to rated amp-hour capacity. See Battery C-rate Explained.
OCV — Open-circuit voltage
Terminal voltage measured without an applied load after an appropriate rest.
CCV — Closed-circuit voltage
Voltage while current is flowing; it includes internal voltage drop.
ESR — Equivalent series resistance
A simplified resistance representing instantaneous internal losses. See Internal Resistance.
State and life
SOC — State of charge
An estimate of the charge remaining relative to a defined full state.
SOH — State of health
An estimate of present capability—such as capacity or power—relative to a reference condition.
DoD — Depth of discharge
The fraction of capacity removed from a defined full state.
Cycle life
The number of defined cycles completed before reaching a specified end-of-life criterion. See Cycle Life.
Calendar life
Service loss caused by elapsed time, including periods when the battery is unused.
Self-discharge
Loss of stored charge while disconnected from an external load.
Charging and packs
BMS — Battery management system
Electronics that monitor, estimate and enforce battery operating limits. See BMS Explained.
CC-CV — Constant current–constant voltage
A common lithium-ion charging method. See Lithium-ion Charging.
Cell balancing
Reducing state-of-charge differences among series-connected cell groups.
Nominal voltage
A representative label used to classify a cell or pack, not a fixed operating voltage.
Internal resistance
Opposition inside a battery that causes voltage drop and heating when current flows.
Energy and safety
Energy density
Stored energy divided by mass or volume.
Power density
Power capability divided by mass or volume.
Thermal runaway
A self-accelerating heat-release process in which rising temperature drives reactions that produce still more heat. See Lithium-ion Safety.