Nominal capacity is a labeled or rated capacity value used as a standard reference under defined conditions. In EV and charging contexts, it most commonly refers to:
– Battery nominal capacity: the rated energy capacity of a battery (usually in kWh) under specified test conditions
– Electrical equipment nominal capacity: the rated capacity of equipment such as chargers, cables, switchgear, or transformers (kW, A, or kVA)
Nominal values are used for comparison and design, but real-world performance can differ due to operating conditions and system limits.
Nominal capacity in EV batteries
For EV batteries, nominal capacity is the stated energy the battery can store:
– Expressed in kWh and determined by cell chemistry, configuration, and test methods
– Often differs from usable capacity, because manufacturers reserve buffer at the top and bottom of the state-of-charge window to protect battery life
– Can change over time due to degradation and temperature effects
Key distinctions:
– Nominal capacity: rated battery energy under defined conditions
– Usable capacity: energy accessible for driving and charging (what drivers effectively get)
– State of health (SoH): how much capacity remains relative to new
Nominal capacity in EV charging infrastructure
Nominal capacity is also used in electrical design:
– Charger nominal power (e.g., 11 kW, 22 kW, 150 kW) may not always be delivered due to vehicle limits, site constraints, or thermal derating
– Transformer nominal capacity (kVA) and feeder ratings define maximum continuous loading under standards
– Cable and protection device nominal ratings must match expected load and installation conditions
Why nominal capacity matters
Nominal capacity is central to sizing, planning, and reporting:
– Helps compare vehicles, chargers, and infrastructure options consistently
– Drives charging time estimates (kWh to deliver vs available kW)
– Supports site capacity planning, including maximum site demand and diversity factors
– Impacts billing and reporting (kWh delivered vs pack capacity, utilization metrics)
– Influences fleet readiness planning (required energy per shift vs charging window)
Common pitfalls and misunderstandings
– Assuming nominal battery capacity equals usable driving energy
– Assuming nominal charger power equals delivered power in every session
– Ignoring temperature, cable length, ventilation, and thermal derating effects
– Overlooking site constraints (load management, demand limits) that cap available power
– Mixing kW (power) and kWh (energy) when estimating performance
Related glossary terms
Usable capacity
State of Charge (SoC)
State of Health (SoH)
Charging curve
Peak charging power
Maximum site demand limit
Load management
Transformer capacity
kWh delivered per charger
Degradation mitigation