This post demonstrates the procedure to test the capacity of a battery. The test will determine and compare the battery’s real capacity to its rated capacity.

A load bank, voltmeters, and an amp meter will be utilized to discharge the battery at a specific current till a minimum voltage is achieved.

The findings will be recorded across time intervals to determine whether the battery matches the required amp-hour rating according to discharge current & duration.

There are unique discharge processes for each battery model to verify their capacity in accordance with manufacturer norms and specifications.

**Scope **

Test the capacity of **batteries.**

**Test Purpose**

The purpose of this test is to compare the battery’s real capacity to its rated capacity.

**Reference **

Refer to applicable manufacturing standards, contract specifications, and construction drawings.

**Battery Preparation**

- To prepare the battery, measure and record the open circuit voltage of each cell or unit to ensure a minimum permissible voltage before interconnecting.
- Connect individual cells/units using the application-specific cables or
**busbars** - To ensure full charge, equalize the battery for 24 hrs at the appropriate voltage.
- After equalization, float charge the battery at the appropriate voltage for 3-7 days before acceptance testing.
- Before starting the acceptance capacity test, measure &Â record individual cell/unit float voltages.

**Equipment Requirements**

- Load bank capabilityÂ of delivering the required discharge current.
- Use digital voltmeters to check entire battery discharge voltage.
- Use an amp meter to check battery discharge current.
- Use a digital voltmeter to check individual cell/unit voltages undergoing discharge.
- Use a stopwatch to check discharge time.

**Test Conditions**

Brand:

Manufacturer:

Model:

Rated Capacity:

Voltage per cell:

Design Life:

Quantity per Bank:

Discharge Current:

End Voltage:

Time:

Temperature: ____Â°C.

**Test Procedure**

**Step-1:** Ensure instrumentation is operational & properly connected to the battery for continuous monitoring of discharge voltage and current.

**Step-2:** Measure the float voltage of the each cell/unit to ensure appropriate flotation.

**Step-3:** Disconnect the charging current from battery.

**Step-4:** Connect the load bank to the battery when it is powered off.

**Step-5:** Start the timer and activate the Load Bank, adjusting and maintaining the optimum discharge rate.

**Step-6:** Record battery discharge voltage, current, & time at the start & the end of the test, as well as at regular intervals throughout the test.

**Step-7:** End the capacity test when the battery reaches the predetermined end point voltage (1.8V), a cell (or) unit reverses, or a safety issue is identified.

**Calculation Requirements**

- The ampere-hour rating is calculated by multiplying the number of amperes of current that the battery can supply by the number of hours it takes to reach a specific end point voltage.Â
- For an accurate current determined during the test, the time of the test should match the calculation.

**Test Record**

30 seconds | 1h | 2h | 3h | 4h | 4.5h | 5h | ||

Battery Voltage (V) | 108 |

Tested by | Verified by | Supervised by | ||

Signature | ||||

Name | ||||

Date |

**Battery Capacity Calculation Methods**

With the test above, you can calculate your demonstrated capacity. It can be calculated in two ways:

- Rate Adjusted Method
- Time Adjusted Method

**Rate Adjusted Method**

When testing for less than an hour, always utilize the rate-adjusted approach. For durations of one hour or more, either the rate adjusted or time adjusted technique can be applied. **IEEE 450** and **IEE****E 1188** provide a full explanation of the rate adjusted approach, with examples.Â

**Time Adjusted Method**

The time-adjusted technique is recommended since it is easier to calculate while remaining accurate.

See the time-adjusted approach that follows:

**Battery Temperature as 25Â°C**

To compute % capacity using the time adjusted technique, divide actual discharge time by the rated time, then multiply by 100. This assuming the battery is at 25Â°C.

**Formula:** % Capacity = T_{a}/T_{s} x 100

Where

T_{a }– Actual Test Time

T_{s} – Rated Test Time

**Battery Temperature is not as 25Â°C**

When the battery temperature is not as 25Â°C, use a barely modified formula utilizing a temperature correction factor (K) from the corresponding IEEE standard.

**Formula:** % Capacity at 25Â°C = [T_{a}/ (T_{s} x K_{t})] x 100

Where

T_{a }– Actual Test Time

T_{s} – Rated Test Time

K_{t} – temperature correction factor based on the applicable **IEEE standard**.