Nominal Cell and Pack Voltage
Nominal voltage is a representative voltage used to describe a battery cell or pack. It is a rating and calculation reference, not the voltage the battery maintains at every state of charge or operating condition.
Cell nominal voltage
A cell's terminal voltage changes as it charges and discharges. Chemistry, electrode design, state of charge, current, temperature, internal resistance, and ageing all affect the measured value.
The nominal cell voltage is therefore a conventional representative value within the permitted operating range. Cells with different chemistries can have different nominal, minimum, and maximum voltages even when their physical formats are similar.
From cell voltage to pack voltage
Cells connected in series add voltage. A simplified pack calculation is:
Nominal pack voltage = series cell count × nominal cell voltage
A string of 108 cells rated at 3.7 V nominal is therefore about 399.6 V nominal. Parallel connections add charge capacity and current capability without adding voltage. The complete notation is explained in Series and Parallel Cell Configuration.
Real packs may be divided into modules, branches, or switched sections, and their control systems define minimum and maximum operating limits. See Battery Pack and Configuration for pack configuration.
Nominal is not maximum
An EV described as having a 400 V or 800 V architecture does not necessarily operate at exactly that voltage. These labels often describe an approximate system class. Actual pack voltage moves through a range and can sag under load or rise during charging.
Nominal voltage alone does not reveal:
- Maximum charging voltage
- Charging or discharge power
- Usable energy
- Motor voltage at every operating point
- Compatibility with every charger in the same voltage class
Pack energy is often estimated from nominal voltage and Ampere-Hour (Ah), but a manufacturer-rated or measured energy value also depends on the full voltage curve and defined test boundaries. Battery Basics explains the relationship between voltage, current, charge, power, and energy.