Nominal voltage is derived from the two measured quantities:
V_nom (V) = E_nom (Wh) / C_nom (Ah)
This makes it a calculated average rather than a directly measured value. It represents the mean voltage across the full discharge curve from 100% to 0% state of charge under standard conditions, not the voltage at any particular point during operation.
Nominal vs operating voltage
Cell voltage is not constant during use. It varies continuously with state of charge, discharge rate, and temperature. At the start of a discharge the terminal voltage sits close to the upper cut-off voltage; it then follows the discharge curve profile — sloped for NMC and NCA, flat-plateau for LFP — before dropping sharply as the lower cut-off is approached. The nominal voltage sits somewhere in the middle of that range and is only encountered briefly during a real discharge cycle.
This distinction matters in pack design. Component voltage ratings, inverter input ranges, and BMS thresholds must be set against the full operating voltage window — from maximum charge voltage to minimum discharge cut-off — not against the nominal value alone.
Chemistry reference values
Nominal voltage is primarily determined by electrode chemistry:
| Chemistry | Nominal Voltage | Max Charge Voltage | Min Discharge Voltage |
|---|---|---|---|
| NMC / NCA | ~3.6 V | 4.1 to 4.25 V | 2.5 to 3.0 V |
| LFP | ~3.2 V | 3.5 to 3.8 V | 2.5 V |
| LTO | ~2.3 V | 2.85 V | 1.5 to 1.8 V |
| Lead acid | ~2.0 V | 2.25 to 2.45 V | 1.75 V |
Upper voltage limits vary between cell designs within the same chemistry family and must be confirmed from the manufacturer’s datasheet.
Scaling from cell to pack
Pack nominal voltage is determined by the number of cells in series:
V_pack = V_cell_nom × N_series
Common automotive architectures target 400 V or 800 V nominal, which with an NMC cell at 3.6 V nominal requires approximately 111s or 222s cells in series respectively. BESS applications span a much wider range depending on the inverter topology and grid connection voltage.
Nominal Voltage Distribution vs BESS Application Type
The chart illustrates how pack nominal voltage scales with application type. Residential and telecom systems cluster at lower voltages — typically below 100 V — while commercial and grid-scale installations operate at 500 V and above, driven by the efficiency advantages of high-voltage DC architectures and the current ratings of available power electronics.
The spread within the Home and Telecom categories reflects the variety of legacy and retrofit configurations in those markets.
For the relationship between nominal voltage, capacity, and energy at cell and pack level, see Nominal Capacity and Nominal Energy. For pack voltage architecture trade-offs, see 800V Architecture.