Internal Ohmic Measurement vs. Capacity Testing – 4 Key Differences

Power storage can be a complicated industry with complicated vocabulary, but have no fear! Power Storage Solutions is here to break down common questions and provide insight into the basics of the vernacular. Today, we’ll dive into internal ohmic measurement, capacity testing, and differences between the two. Without further ado, let’s get into it!

What is Internal Ohmic Measurement?

Internal ohmic measurement, also known as impedance, conductance, or resistance testing, is used to assess the internal health of a battery.

It involves applying a small, known alternating current (AC) or direct current (DC) signal to the battery terminals and measuring the voltage response. By analyzing the phase shift and magnitude of the voltage and current, the internal ohmic of the battery can be calculated and compared to baseline (if known) of the originally installed product.

Internal ohmic measurement provides insight into the condition of the battery, including its resistance to current flow. High internal resistance can indicate issues such as sulfation, plate degradation, or electrolyte problems. It is a quick and non-destructive method for assessing battery health. It can detect problems early and help prevent unexpected battery failures.

What is Capacity Testing?

Capacity testing is used to determine the actual storage capacity of a battery, i.e., how much energy it can store and deliver under specific conditions.

Capacity testing typically involves fully charging the battery and then discharging it at a constant rate while measuring the total energy output. The discharge process may be conducted until a certain endpoint voltage is reached or until the battery’s voltage drops below a specified threshold.

Capacity testing provides information on the battery’s ability to store and deliver energy over time. It is the best and, in our opinion, the ONLY true way to help determine if the battery can meet its specified performance requirements and if it has degraded over its lifespan.

Capacity testing is essential for assessing battery performance accurately, especially in applications where reliable energy storage is critical, such as in backup power systems or electric vehicles. It can identify capacity loss due to factors like sulfation, plate degradation, or electrolyte depletion.

What’s the Difference?

• Internal ohmic measurement focuses on assessing the internal resistance of the battery, while capacity testing evaluates its energy storage capacity.
• Internal ohmic measurement involves applying an AC signal and analyzing the voltage and current response, while capacity testing involves fully charging and discharging the battery to measure its total energy output.
• Internal ohmic measurement provides insight into the battery’s internal condition and resistance, while capacity testing assesses its ability to store and deliver energy.
• Internal ohmic measurement is often used for quick diagnostics and monitoring of battery health and can be a good trending tool for determining when a capacity test might be recommended, while capacity testing is essential for evaluating battery performance and lifespan, especially in critical applications.

IEEE, NERC, and battery manufacturers all agree that capacity testing is the only method to accurately measure a battery system’s true capacity. It determines the state of health of the batteries by assessing their ability to deliver power when needed. All manufacturers agree to warranty a battery after a capacity test is performed. While some manufacturers may warranty based upon a deviation from the baseline of ohmic readings.

In summary, both internal ohmic measurement and capacity testing are valuable tools for assessing lead-acid battery health and performance, each providing unique insights into various aspects of battery behavior.

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