What Is the Difference Between Nominal Voltage and Working Voltage?
Nominal voltage is a rounded label used to classify a cell, while working voltage is the real voltage that changes continuously as the battery charges, discharges and rests.
The key voltage points
A typical lithium-ion cell has a nominal voltage of 3.6 to 3.7 V. It starts near 4.2 V when fully charged, the upper cut-off, settles around 3.7 V under moderate load, and falls toward 2.5 to 3.0 V when empty, the lower cut-off. The open-circuit voltage, measured at rest with no current, sits between these values and reflects state of charge.
Why it matters for design
Equipment electronics must tolerate the full working range. A device rated for 3.7 V nominal still receives 4.2 V at full charge and may brown out near cut-off. When packs are built in series, nominal voltage multiplies; a 4S pack is about 14.8 V nominal but ranges from roughly 12 V to 16.8 V.
In short
Use nominal voltage to compare and label cells, but design against the actual charge and discharge cut-off window to ensure your circuit works across the whole state-of-charge range.