How to measure the actual capacity of the battery?

Test methods are estimating the battery conditions, yet capacity testing of the battery is the authentic way of determining the support that the battery will offer. Battery capacity testing allows knowing the battery performance and its life, besides identifying weak cells.

The battery capacity informs the electrical energy general as the total amount by electrochemical reactions. It is expressed in amp-hours or watt-hours. Battery capacity is the electricity shown as the total amount that the battery produces due to the electrochemical reactions from within.

A battery capacity changes as per the structure, age, size, and density of an electrolyte. It causes excessive heat that the lead grates experience wear on lead acid batteries.

However, the battery curves of charge and discharge are exponential. The battery capacity is measured in (Wh) Watt-hours. It is the voltage variation while there is discharge in the battery. Thus, the proxy for capacity is Ampere Hour (Ah) as the voltage is within the range, so the exact voltage is unimportant to know.

Measuring battery capacity is through these methods:

Constant power?– Hook to a constant current load the battery and measure the time it takes into a specified voltage to drain, but consider using a continuous power load. Wh in capacity- Time in hours x Power in Watts.

Constant current- Hook similarly as above to constant power and measure the battery. The Ah capacity = Time in hours x Current in Amperes.

Constant resistance- The method of constant resistance requires a single resistor- an elementary discharge circuit. Allow the battery discharge by connecting across the battery terminals, the resistor, up to a specific minimum voltage. Now across the resistor, measure the voltage, and take frequent readings. Energy Time x Power and Power V^2/R. Here, time refers to the measurement interval that you calculate, with measurement cycle energy. Add measurements to get Wh, in total capacity.

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Test the internal resistance of the battery to infer the current.

Internal resistance is the opposition to the current flow offered by the batteries and cells. All materials resist to some extent, the current flow, batteries, and cells. The internal resistance depends on the material used in making the batteries.

The elements comprising in making a battery include carbon, zinc, lithium, silver, mercury, etc. Here, not all are good conductors of electricity. Thus, it is hard to find with zero internal resistance a battery or maybe practically impossible. The internal resistance is the battery gatekeeper.

The key point relies on internal resistance and voltage as independent variables. The main thing is the current, the dependent variable that gets affected. The internal resistance is inversely proportional. The voltage decreases with the increase in the internal resistance it is the way to measure the battery's internal resistance.

Internal Resistance in a circuit is from the battery or cell itself. Therefore, with higher internal resistance, the voltage and current are lower.

Use the battery device's built-in test function.

A built-in test or built-in self-test is a mechanism permitting testing a machine by itself. It helps to meet requirements such as lower repair cycle times and high reliability. A built-in test also handles the testing cost during manufacturing and the limited accessibility of technicians.

The built-in test purpose is reducing complexity, thereby reducing dependency on external test equipment and the cost. The built-in test decreases the cost such that:

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It reduces the test complexity by reducing the I/O signals under tester control.

It reduces the duration of the test-cycle.

Built-In-Self-Test helps making it less-expensive, but faster integrated circuit tests in manufacturing. The function of IC verifies a portion or all of the IC's internal functionality, and it is of immense value to customers.

Built-in test equipment includes frequency generators, discharge probes, oscilloscopes, and multimeters. It helps in performing diagnostics and testing. It facilitates individual tests and similar tests.

Battery Capacity and Electrolyte Specific Gravity

Electrolyte specific gravity in a battery falls between 1.000 and 1.835. This is because a lead-acid battery electrolyte consists of sulfuric acid and water as a mixture. Normally, a battery electrolyte is mixed so that the specific gravity does not surpass 1.350.

The electrolyte is 1.26 times in a fully charged battery, and the weight is similar to taking pure water in equal volume when the liquids are in the same temperature. Therefore the battery electrolyte showing 1.260 is ‘Specific Gravity’ because its weight is the pure water weight 1.260 times. The specific gravity measurement is done using a hydrometer.

A hydrometer is within a glass tube, as a glass float. It is sealed at both ends. Along the floating body, in specific gravity, a scale is calibrated positioning it lengthwise. The float is within the glass tube, and within the tube the fluid to test is drawn. Once the fluid into the tube is drawn, the hydrometer float sinks in the fluid to a particular level. The fluid’s specific gravity is when the hydrometer float comes above the fluid level. The float scale reading at the fluid surface is the fluid-specific gravity.

Specific gravity is an indicator of the charge state in a cell or battery. Nevertheless, the measurements of specific gravity do not determine the capacity of a battery. The direct and authentic way of testing the charge state of a battery is by determining the specific gravity of a battery electrolyte. The specific gravity is higher of the electrolyte when the state of charge is higher.

Increasing a battery’s specific gravity, implies adding to the battery cells more electrolyte solution. The specific gravity is a measure of a battery’s electrolyte with the density in comparison to the water, and thus, it affects the performance of a battery directly. The specific gravity when fully charged ranges from 1.270 to 1.305. The same when fully discharged, may vary between 1.097 and 1.201.

Final Thoughts

An electrolyte transfers ions and is a battery component, carrying particles as charge front and back between the two electrodes in a battery, thereby causing the battery to discharge and charge. However, the lithium-ion batteries today feature well-defined electrolyte chemistry.