How to Calculate Battery Internal Resistance and Its Effect on Power Delivery

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Understanding the internal resistance of a battery is essential for assessing its performance and efficiency. It affects how much power the battery can deliver and how quickly it discharges. This article explains how to calculate internal resistance and its impact on power delivery.

Calculating Internal Resistance

The most common method involves measuring the voltage and current during a load test. By applying a known load, you can determine the voltage drop across the battery and calculate the internal resistance.

The formula used is:

Rinternal = (Vno load – Vload) / I

Where:

  • Vno load = Voltage without load
  • Vload = Voltage under load
  • I = Current during load

Impact on Power Delivery

Internal resistance causes voltage drops when the battery supplies current. Higher resistance results in lower voltage at the terminals, reducing the power delivered to the load.

The power delivered can be calculated using:

P = Vterminal × I

Where Vterminal = Vno load – (I × Rinternal)

Factors Affecting Internal Resistance

Several factors influence internal resistance, including:

  • Battery age and usage
  • Temperature
  • State of charge
  • Battery chemistry