Use this engineering calculation for a transparent preliminary estimate or independent arithmetic check when geometry, materials, loads, operating conditions, and units are defined consistently.

Open Circuit Volts (V)

Required number input.

Loaded Volts (V)

Required number input.

Current Amperes (A)

Required number input.

Apparent battery DC internal resistance from open-circuit and loaded terminal voltages at a measured discharge current. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Resistance Ohms (Ω)

The resulting resistance ohms returned as a number.

• Battery voltage, capacity, resistance, state of charge, and energy density depend on chemistry, series-parallel topology, temperature, rate, cutoff, balance, aging, and measurement method. Cell mismatch and protection limits must be evaluated separately.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Check assumptions against drawings, measurements, current material data, and the applicable design code. Apply required load combinations and safety factors, then obtain qualified review and testing for consequential designs.

• Battery SOC Coulomb

  Ideal battery state of charge after a constant discharge current, using nominal amp-hour capacity; ignores coulombic losses and aging.

• Short Circuit MVA

  Balanced three-phase fault apparent power in MVA from line-to-line voltage in kV and fault current in kA.

• Critical Depth Rectangular

  Critical depth of rectangular open-channel flow from unit-width discharge q: yc=(q²/g)^(1/3).