Ohm’s Law

The fundamental relationship between a cell’s open circuit voltage, internal resistance, and terminal voltage under load. The most-used equation in pack electrical design. See the Thevenin Model for how internal resistance is modelled in more detail, including its split into ohmic and polarisation components.

Vt=OCV−(IRint)V_t=OCV-(IR_{int})

Where:

  • Vₜ = terminal voltage (V) — voltage at cell terminals under load
  • OCV = open circuit voltage (V) — equilibrium voltage at rest
  • I = current (A) — positive for discharge, negative for charge
  • Rint = internal resistance (Ω)
  • On charge: Vₜ = OCV + (I × Rint)

See also: Kirchoff Laws, Watt Hour