The vented nickel-cadmium battery acceptance test is an electrical and physical examination of a new or reconditioned nickel-cadmium battery bank intended for DC system service - such as control power, emergency lighting, or uninterruptible power-supply applications - before it is energized and connected to its charger and load. NETA ATS-2025 Section 7.18.1.2 calls for a suite of checks that includes visual inspection for mechanical damage or corrosion, measurement of the open-circuit voltage of the string and of individual cell voltages, a load test to verify the battery can sustain the required discharge current for the specified time window under stated conditions, and confirmation that all terminals and inter-cell connectors are clean and tight. The test is performed on the complete assembled battery string, one cell or section at a time where direct access is available, with the battery isolated from any charging source during measurement.
A nickel-cadmium battery only performs its duty - supplying DC power to critical loads during a mains outage or providing the steady trickle charge to a control circuit - if its cells are intact, its inter-cell and terminal connections are secure and corrosion-free, and its total capacity matches the design specification. Damage in transit, manufacturing defects, or incomplete assembly can compromise capacity or raise the risk of an inter-cell short circuit that would not show up in a simple voltage check. A load test forces the battery to discharge under representative load and confirms it can sustain that discharge for the required duration without voltage sag below limits; a battery that fails this test before it enters service prevents a downstream failure that would leave the protected system without backup power during an actual outage.
Acceptance testing is performed on a new or reconditioned battery bank before it is first connected to its float charger and placed into service. The battery must be fully assembled and floated at rated voltage for a period - often 24 hours or longer - before the acceptance test begins, so the cells reach equilibrium and residual charge is established. If a battery is damaged in shipping or has been stored out of service for an extended period, the acceptance test is repeated to confirm it has recovered and is fit for duty.
With the battery isolated from its charger and load, the test begins with a visual walk-down of the entire string, documenting the condition of each cell case, terminal, and connector and noting any signs of corrosion, seepage, or mechanical damage. Open-circuit voltage is measured across the entire string with a calibrated digital voltmeter, recorded alongside the ambient temperature, and then individual cell voltages are measured across each cell terminal pair in sequence. Next, the battery is subjected to a load test: a calibrated load bank or resistive load is connected to the battery terminals, set to draw a current matching the design discharge current, and the voltage at the battery terminals is monitored throughout the discharge duration specified for that battery type and system voltage. The voltage is recorded at regular intervals - often every 5 or 10 minutes - and the test is stopped when either the specified duration has been met or the terminal voltage drops below the minimum acceptance threshold, whichever comes first. After the load test, the battery is allowed to rest and then floated back to rated voltage on its normal charger before it is connected to the system.
Open-circuit voltage of the string and the individual cell-voltage readings for each cell, ambient temperature and relative humidity at the time of measurement, the calibrated test instrument identification (make, model, serial number, calibration due date), load-test discharge current and duration, terminal voltage readings taken at specified intervals during the load test, the time at which the test was terminated, and any notes or deficiencies noted during the visual inspection or load-test execution. If a cell is found to be out of specification, its location, voltage, and the action taken (rejection, cell replacement, or monitoring) are recorded.
NETA ATS-2025 7.18.1.2 sets forth the acceptance criteria in both tabular and narrative form. Open-circuit voltage for the string shall not deviate from the nominal system voltage by more than a narrow margin established for the battery chemistry and nominal voltage - for a vented nickel-cadmium string, this is typically a small positive and negative tolerance around the nameplate value. Each individual cell voltage is checked against a per-cell minimum that reflects the chemistry and state of charge at test time; a cell reading below that minimum indicates a shorted or failed cell and requires investigation before the battery is placed in service. The load test acceptance criterion specifies that the battery terminal voltage must remain above a stated threshold throughout the discharge period and until the specified time has elapsed; if voltage drops below that threshold before the time window is complete, the battery capacity is insufficient and the battery shall be rejected or refurbished. All inter-cell connectors and terminals must be visually clean and tight, and any visible corrosion or leakage must be remedied before the battery is energized. See the purchased NETA standard for the complete voltage tolerances, per-cell minimums, and load-test acceptance thresholds by system voltage.
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