DC Battery Systems

This specification covers stationary battery systems consisting of a battery (one or more series strings of cells), one or more battery chargers, a DC distribution panel, and the associated monitoring, alarms, room ventilation, and spill containment, intended to supply 24, 48, 125, or 250 nominal volts DC to critical control and protection loads. Equipment and installation shall comply with the referenced IEEE standards for the selected chemistry and with NFPA 70 Article 480 for the storage battery installation. Where the project is a substation or generating station under the exclusive control of an electric utility, the utility's adopted edition of IEEE C2 (National Electrical Safety Code) governs and the present standard shall be applied in a manner consistent with that code.

A DC battery system is a continuously available source whose first job is to operate switchgear protective relays, trip and close coils, and emergency control loads when the AC supply is disturbed or absent. The system is therefore designed for the worst-case duty cycle that can occur during an AC outage — including momentary inrush from breaker close coils — and not for an average load. The Contractor and the Engineer shall treat the duty cycle, not the steady float current, as the basis of design.

This standard does not cover lithium-ion energy storage systems intended for grid-side or behind-the-meter energy applications; those systems trigger the full NFPA 855 / UL 9540 code stack and shall be specified separately. The narrow utility-style lithium chemistries that may be used as a direct replacement for a VRLA control battery are an emerging case; where such a system is proposed, the requirements of NFPA 855 and UL 9540 / UL 1973 shall be applied in addition to this standard, and the Engineer of Record shall confirm the listing and the local AHJ position before procurement.

Grounding of the DC system and bonding of the battery rack and enclosures shall be in accordance with Grounding And BondingGrounding and Bonding for Electrical SystemsResolves to the current adopted revision.sync/grounding-and-bonding. The protective devices and control loads that the DC system supplies shall be coordinated with Low Voltage SwitchgearLow Voltage SwitchgearResolves to the current adopted revision.sync/low-voltage-switchgear and Medium Voltage SwitchgearMedium Voltage SwitchgearResolves to the current adopted revision.sync/medium-voltage-switchgear.

Equipment, materials, and installation shall comply with the latest adopted edition of the following standards and codes. Where the contract documents, the adopted building code, or a referenced standard conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.

Contractor shall submit the following for the Engineer's review prior to fabrication and procurement. No portion of the DC system shall be ordered or installed before the corresponding submittals are reviewed and returned.

• Battery sizing calculation per IEEE 485 (lead-acid) or IEEE 1115 (Ni-Cd), showing the assumed duty cycle, end-of-discharge voltage, design margin, aging factor, and temperature correction factor
• Charger sizing calculation per IEEE 946, showing the assumed continuous DC load, recharge current, and recharge time
• Product data for the cells or monoblocs, the charger(s), the DC distribution panel, the battery rack, the battery monitor, and the spill containment system
• Shop drawings showing the battery rack elevation, cell or jar arrangement, charger and DC panel locations, conduit and cable routing, and clearances in the battery room or cabinet
• One-line diagram of the DC system showing the battery, the charger(s), the DC distribution, downstream protective devices, and all monitoring and alarm points
• Cable sizing calculations including ampacity, voltage drop, and short-circuit withstand for the battery cables and DC feeders
• Ventilation calculation per IEEE 1635, showing the assumed hydrogen evolution rate, the required dilution airflow, and the air-change rate or sustained ventilation rate
• Seismic certification documentation for the battery rack and the charger, where required by the applicable building code
• Manufacturer's installation instructions for the cells, the rack, and the spill containment system

Contractor shall provide the following at substantial completion before the DC system is accepted into service.

• Operation and maintenance manuals for the battery, the charger, the DC panel, and the monitoring system
• Acceptance test reports per IEEE 450 or IEEE 1188 (lead-acid) or IEEE 1106 (Ni-Cd), signed by the testing technician
• Initial commissioning test report including the load test or modified performance test, charger functional test, and alarm verification
• As-built drawings reflecting the installed battery configuration, cell numbering, polarity, and cable terminations
• A baseline record of intercell connection resistances, individual cell or monobloc float voltages, and individual cell or monobloc internal resistance or conductance
• Warranty documentation from the cell manufacturer and the charger manufacturer
• A recommended maintenance schedule keyed to IEEE 450, IEEE 1188, or IEEE 1106 as applicable
• A copy of the safety data sheet for the electrolyte

Cells, chargers, and racks shall be supplied by manufacturers regularly engaged in the production of stationary battery systems for utility, substation, or industrial control applications, with a minimum of five years of documented experience in the specified chemistry. The cell manufacturer shall publish performance data (capacity versus discharge rate, capacity versus temperature, float current, and expected service life) for the specific cell type proposed.

The cells of a single battery shall be from a single manufacturer, of a single type and design, and of a single date code or production lot to the extent practical. Mixing of cell types, ages, or capacities within a single battery is not permitted, because cells with different characteristics in series will not share the load uniformly and the weakest cell will dictate the battery's performance and life.

Acceptance and performance testing shall be performed by a firm regularly engaged in testing stationary batteries, employing technicians trained in the test procedures of IEEE 450, IEEE 1188, or IEEE 1106 as applicable to the chemistry. Testing personnel shall demonstrate experience with the discharge load bank, the cell-voltage data acquisition system, and the manufacturer's specific procedures for the cells being tested.

The charger shall be listed and labeled to UL 1989 by a Nationally Recognized Testing Laboratory. The DC distribution panel and DC overcurrent devices shall be listed for DC service at the system voltage. Cells and monoblocs shall be listed to UL 1973 where required by the AHJ or the applicable code; in traditional substation control applications the AHJ commonly accepts cells designed and manufactured to the relevant IEEE recommended practice without separate UL listing, and the Engineer of Record shall confirm the local position before procurement.

Battery performance is strongly dependent on temperature. The Engineer shall establish the design ambient temperature range of the battery room or cabinet, and the Contractor shall apply the corresponding temperature correction factor in the sizing calculation. The room or cabinet shall be conditioned and ventilated to keep the battery within the temperature range used for sizing and for service-life prediction.

The reference temperature for stationary battery capacity ratings is 25°C (77°F). Capacity decreases at lower temperatures and increases (with accelerated aging) at higher temperatures. A battery sized at 25°C and installed in an unconditioned space that routinely operates at 10°C may deliver substantially less than its rated capacity at the time it is most needed. Conditioning the battery space to the reference temperature is, in most cases, less expensive over the life of the system than the cell oversizing required to compensate for cold operation.

The Contractor shall apply a temperature correction factor in the sizing calculation, taken from the cell manufacturer's published data or from the tables in IEEE 485 (for VLA) or IEEE 1115 (for Ni-Cd). The correction is applied to the minimum expected battery temperature during a discharge, not the average. A 125 VDC station battery sized for a 25°C room but allowed to drop to 0°C during a winter outage will see roughly a 20–25 percent capacity reduction at the moment of discharge and shall be sized accordingly.

The multipliers above are representative of vented lead-acid cells discharged at moderate rates; the Contractor shall use the cell manufacturer's published correction factor for the specific cell type, discharge rate, and end-of-discharge voltage of the project duty cycle.

Lead-acid float current and the rate of grid corrosion roughly double for every 10°C above 25°C, so a VRLA battery operated continuously at 35°C will reach end of life in approximately half the service hours of one operated at 25°C. Battery space cooling shall keep the maximum continuous cell temperature at or below 25°C where the published design life is to be achieved.

Stationary battery performance is not strongly altitude-dependent within the range of typical installations. Charger output ratings shall be confirmed for the installation altitude per the charger manufacturer's data. Battery rooms shall be kept dry; standing water or persistent high humidity accelerates corrosion of intercell connections and of the rack itself.

Where required by the applicable building code, the battery rack and the charger shall be seismically certified by shake-table testing per ICC ES AC156 or by analysis per ASCE 7. The rack shall be designed to retain the cells during a seismic event without damaging the intercell connectors or the cell jars. Site-specific anchorage shall be designed by the Engineer of Record and shown on the contract drawings.

The chemistry decision drives almost every downstream requirement in this standard: cell sizing method, charger float voltage, ventilation, spill containment, room layout, monitoring strategy, maintenance interval, and design life. The Engineer shall make this selection early in design.

Vented lead-acid (VLA) cells offer the longest published design life (commonly 20 years), the most predictable end-of-life behavior, and the longest history of utility service, at the cost of higher ventilation requirements during charging and equalize, mandatory electrolyte maintenance, and the largest room footprint per kilowatt-hour of stored energy.

Valve-regulated lead-acid (VRLA) cells eliminate routine electrolyte maintenance and produce far less hydrogen under normal float operation, allowing more compact installations and use in cabinets rather than dedicated rooms. They are, however, less tolerant of high temperatures than VLA, more difficult to assess by float voltage alone (because the recombination chemistry masks the symptoms of a failing cell), and have a shorter published design life — typically 10 to 15 years for "long-life" telecom-grade product, and as short as 5 to 8 years for general-purpose VRLA installed in poorly conditioned spaces.

Vented nickel-cadmium (Ni-Cd) cells tolerate a wider temperature range, tolerate deep discharge and partial-state-of-charge operation without measurable harm, and resist thermal runaway in service. They are correspondingly more expensive per kilowatt-hour, require a higher number of cells for a given nominal voltage (because of the lower per-cell voltage), and require different charger float and equalize voltages. Ni-Cd is the conventional choice for outdoor cabinets in extreme climates and for installations where occasional deep discharge is expected.

Lithium-ion is included as an option for completeness; specifying lithium-ion brings NFPA 855 and UL 9540 into scope and is outside the typical "control battery" application. Lithium-ion in this application shall not be selected without explicit AHJ confirmation and a separate hazard mitigation analysis where required.

Nominal DC voltage is dictated by the connected protective relays, breaker close and trip coils, communications equipment, and any inverter loads. 125 VDC is the predominant voltage for medium-voltage and large low-voltage switchgear control in North American utility and industrial practice. 250 VDC is used at larger generating stations and where long DC cable runs to remote switchyards make a higher voltage economical. 48 VDC is the predominant voltage for telecommunications, smaller distribution substations, and packaged equipment. 24 VDC is used for small local control applications.

End-of-discharge (EOD) voltage is the minimum cell voltage at which the connected loads will still operate correctly. It is set by the lowest-voltage-tolerant load in the DC system — typically a protective relay, an inverter, or a breaker close coil — and must be agreed with the Engineer before sizing. A lower EOD allows a smaller battery (because more of the cell's capacity is usable) but increases the risk that a load drops out before the duty cycle ends; a higher EOD is conservative but increases cell count and size. The EOD set in the sizing calculation shall be the same EOD used to determine the minimum system voltage at the end of the duty cycle, accounting for cable voltage drop between the battery terminals and the most distant load.

The battery shall be sized to supply the specified duty cycle, at the end-of-discharge voltage, at the minimum design temperature, at end of life, with the specified design margin. Sizing shall follow IEEE 485 for lead-acid (VLA or VRLA) and IEEE 1115 for Ni-Cd. The Contractor shall submit the calculation showing each factor explicitly.

The duty cycle is a time-versus-load profile that begins at the loss of charger output and continues through the longest expected period without recharge. The duty cycle shall include three load classes per IEEE 946:

• Continuous loads that are present throughout the duty cycle — indicating lamps, relay holding currents, communications power, supervisory relays
• Noncontinuous loads energized for a defined portion of the duty cycle — emergency lighting transfers, motor-operated valves, recloser operations, alarm pickup
• Momentary loads, with a duration not exceeding one minute, that produce a sharp inrush — circuit breaker trip and close coils, lockout relay coils, SCADA contactor pickups

The momentary load at the end of the duty cycle is typically the sizing driver for a control battery, because the cell voltage is lowest then and the inrush is highest. The duty cycle shall explicitly include at least one breaker close operation at the end of the discharge.

Eight hours is the predominant duty cycle for unattended distribution substations because it brackets the time to dispatch a repair crew and restore station service. Attended generating stations and stations with redundant station service may use shorter cycles; remote sites with long restoration times use longer cycles. The Engineer shall set the duty cycle from the facility's operating concept, not from a table default.

The complete time-versus-load duty cycle shall be as indicated on the DC system duty-cycle diagram.

The design margin accounts for load growth and for inaccuracies in the load tabulation. A new substation with a fully developed relay and control schedule may use 10 percent; a battery in a building where future loads are likely to be added to the DC panel shall use 20 to 25 percent. Design margin is applied to the calculated cell size, not to the cell quantity.

A lead-acid cell's capacity is relatively flat through most of its life and then drops at end of life. IEEE 485 defines end of life as the point where the cell delivers 80 percent of its rated capacity; the corresponding aging factor of 1.25 (1.00 / 0.80) ensures the battery still supplies 100 percent of the design duty cycle at end of life. Ni-Cd cells age more gradually and IEEE 1115 commonly uses 1.10 to 1.15. Sizing without an aging factor presumes the battery will be replaced at the first sign of capacity loss; this is operationally impractical for utility-style installations and shall not be used.

Temperature correction shall be applied per the manufacturer's published data or per IEEE 485 / IEEE 1115 tables, using the minimum design temperature of the battery space during a discharge. See the Environmental and Service Conditions section above for representative multipliers.

Published design life is achieved at the reference temperature (25°C) under recommended float charge with the manufacturer's recommended maintenance. Actual service life depends on the operating temperature, the cycling history, and the quality of maintenance. The Engineer shall coordinate the design life with the Owner's asset-management horizon — a 20-year design life is undermined by a maintenance program that cannot survive the first ownership change.

Lead-calcium grids reduce gassing and water loss compared to lead-antimony, making them the conventional choice for modern stationary VLA cells; lead-antimony is more tolerant of cycling and is sometimes specified for batteries that see frequent discharge. AGM and gel are both VRLA constructions; AGM is the predominant choice for substation control and has better high-rate performance, while gel is sometimes preferred for hot environments because of its lower water loss. Pocket-plate Ni-Cd is the conventional substation choice in cold climates; fiber- and sintered-plate Ni-Cd offer higher energy density at higher cost.

Cell jars shall be transparent or translucent where electrolyte level is to be inspected visually (VLA, vented Ni-Cd). VRLA monobloc containers shall be flame-retardant per the cell standard. All jar materials shall be resistant to the electrolyte and to the cleaning agents recommended by the manufacturer.

Intercell connectors shall be sized to carry the maximum discharge current at the rated short-circuit fault duration without exceeding the manufacturer's allowable connector temperature rise. Connectors shall be lead-plated copper, copper-clad lead, or solid lead, selected for compatibility with the cell post material. Bolts shall be stainless steel or as supplied by the cell manufacturer.

Each intercell connection shall be installed with the manufacturer's specified anti-corrosion compound on the contact surfaces and shall be torqued to the manufacturer's specified value using a calibrated torque tool. Intercell connection resistance shall be measured and recorded after installation; the baseline values are the reference for all subsequent maintenance testing.

Every cell or monobloc shall be permanently numbered in series order from the positive terminal of the battery. Polarity markings on the positive and negative terminals shall be permanent and unambiguous. A cell numbering and polarity diagram shall be posted at the battery.

The charger shall be a constant-voltage, current-limiting type, suitable for the specified chemistry, listed to UL 1989, and sized to carry the full continuous DC load while simultaneously recharging the battery from a fully discharged state to approximately 95 percent of rated capacity within the specified recharge time.

The IEEE 946 sizing formula for a lead-acid charger is approximately:

Charger output (A) = 1.1 × (continuous DC load in amperes) + (battery capacity in ampere-hours × K / recharge time in hours)

where K is the manufacturer's published recharge factor (often 1.10 to 1.15 for lead-acid). The 1.1 multiplier on the continuous load accounts for charger derating and load growth. A 12-hour recharge time is the predominant value for utility station applications because it leaves substantial margin for a second discharge within the same day. The Contractor shall submit the calculation showing each term.

The float voltage is set to maintain the battery at full charge with minimal water loss and minimal grid corrosion; for VLA at 25°C, this is approximately 2.20 to 2.25 V/cell, depending on the manufacturer. The equalize voltage is a higher setting (approximately 2.30 to 2.40 V/cell for VLA) used periodically to bring lagging cells back into balance after a discharge or to recover from a maintenance event; equalize shall not be applied to a VRLA battery unless specifically permitted by the manufacturer, because the higher voltage increases recombination heat and accelerates dry-out.

Temperature compensation of the float voltage is recommended for installations where the battery temperature varies more than ±5°C from the reference temperature. The compensation slope shall be set per the cell manufacturer's published data; an arbitrary slope can drive the battery into chronic undercharge or chronic overcharge.

A single charger is acceptable for installations where the loss of a single charger is operationally tolerable for the time required to replace it, recognizing that the battery itself continues to supply the loads. Redundant chargers should be specified for installations where the battery duty cycle is short relative to the worst-case charger repair time, or where the AC source for the charger may be lost in the same event that triggers the DC duty cycle. Where two chargers are specified, they should be fed from independent AC circuits so that a single AC outage cannot disable both.

Excessive AC ripple at the charger output accelerates battery grid corrosion and may interfere with sensitive electronic loads. The 2 percent RMS limit is the conventional general-purpose target; lower limits apply where solid-state relays, communications equipment, or sensitive monitoring share the DC bus. Ripple shall be measured at the charger output terminals with the battery connected; ripple measured with the battery disconnected is not representative of normal operation because the battery acts as a filter.

The charger shall provide, as a minimum, the following alarms and indications, wired to dry contacts available at a terminal block for connection to the facility's annunciator or SCADA:

• AC input loss
• High DC voltage
• Low DC voltage
• Ground fault (positive and negative, where the system is ungrounded)
• Charger fail / DC output loss
• Battery on discharge (current flowing out of the battery)

The DC distribution panel takes the charger output and the battery in parallel and distributes them through individually fused or breaker-protected branch circuits to the protective relays, breaker control circuits, inverters, and other DC loads.

A single-bus arrangement is acceptable for installations where the DC system can be taken out of service to address a fault. Dual-bus arrangements are used at large generating stations and critical substations where DC must remain available during maintenance of any single element. The dual-bus topology shall be reflected on the DC one-line diagram and shall be coordinated with the redundancy of the loads themselves.

DC overcurrent devices shall be listed for DC service at the system voltage. AC-rated devices applied to DC service do not extinguish the arc reliably and shall not be used. The interrupting rating shall equal or exceed the maximum short-circuit current available from the battery; battery short-circuit current can substantially exceed the steady-state load current and shall be calculated using the manufacturer's published cell short-circuit data and the battery cable impedance.

A disconnecting means shall be provided in the battery main DC circuit, located within sight of the battery, and shall open both the positive and negative leads, in accordance with NFPA 70 Article 480. The disconnect shall be capable of interrupting the maximum short-circuit current available from the battery.

Substation control DC systems are conventionally ungrounded so that a single ground fault on either bus does not cause a misoperation of a protective relay or a breaker control circuit, and so that an undetected ground fault does not propagate into a phase-to-phase fault inside the control circuits. Ungrounded systems shall be equipped with a continuous ground fault detector that alarms on the presence of a fault to ground on either bus; the detector shall not draw enough current to be itself a hazard if it should fail. Solidly grounded DC systems are sometimes used in industrial DC distribution and in some communications applications, and shall be specified explicitly where used.

DC system grounding shall be coordinated with Grounding And BondingGrounding and Bonding for Electrical SystemsResolves to the current adopted revision.sync/grounding-and-bonding for the bonding of the battery rack, the cabinet, the conduit, and the enclosures of the charger and the DC panel.

Battery monitoring is recommended for any unattended installation and is essential for VRLA installations, because VRLA cells provide no visual cues to a developing fault and float voltage alone is a weak indicator of state of health. Per-cell monitoring with periodic internal-resistance measurement is the most reliable way to identify a failing cell before it fails an in-service discharge. IEEE 1491 provides guidance on selection of battery monitoring equipment.

The monitor shall be wired to the facility's annunciator or SCADA with, at minimum, common-alarm contacts for "battery alarm" and "monitor system fail." Where granular alarming is supported, individual cell-level alarms shall be reported as data points rather than aggregated, so that a developing single-cell failure is visible before it cascades.

For VRLA installations, float current is a leading indicator of thermal runaway: as a VRLA cell dries out, its internal resistance rises and its float current decreases; as a VRLA cell approaches thermal runaway, internal heating accelerates recombination and float current rises sharply. The monitoring system for a VRLA installation should report float current and should alarm on float current exceeding the manufacturer's recommended threshold.

Hydrogen is evolved by all lead-acid and vented Ni-Cd batteries during charging, in proportion to the overcharge current. The hydrogen concentration in the battery space shall be kept below 25 percent of the lower flammable limit, which is 4 percent by volume in air. The conventional design target is 1 percent hydrogen by volume, with 2 percent as the alarm threshold per IEEE 1635.

For VLA batteries and for vented Ni-Cd batteries, mechanical ventilation is the predominant approach in modern installations because the airflow can be sized to a known evolved-hydrogen rate and verified during commissioning. Natural ventilation is acceptable for small VLA installations and for VRLA installations where the hydrogen evolution rate is low and the room volume is large; the Engineer shall confirm that the natural-ventilation airflow at the worst-case wind and temperature condition is sufficient to keep hydrogen below the design target.

A sealed cabinet without forced ventilation is acceptable only for small VRLA installations, where the cabinet design has been evaluated for hydrogen accumulation per IEEE 1635 and the manufacturer's published guidance. Sealed cabinets shall not be used for VLA or vented Ni-Cd installations.

The IEEE 1635 calculation determines the required airflow from the charger output current, the cell finishing current (the fraction of charger current that produces gas at the end of charge), the number of cells, and the room volume, and gives a defensible engineered result. Rule-of-thumb values may be used for small installations but shall not be substituted for the IEEE 1635 calculation in any installation where the AHJ requires a calculation submittal.

A hydrogen detector should be provided in every battery room and battery cabinet where the hydrogen evolution is non-negligible. The detector shall be located near the highest point of the space, because hydrogen is lighter than air and accumulates at the ceiling. The detector's response time and recovery time shall be confirmed against the calculated rate of hydrogen accumulation.

The battery room shall be constructed of materials compatible with the electrolyte and with hydrogen accumulation. Walls and ceiling shall be sealed where necessary to prevent hydrogen leakage into adjacent spaces. Light fixtures, switches, and any other potential ignition sources in the battery room shall be located outside the immediate cell area, or shall be rated for the classified area where the AHJ classifies the space. Electrical conduit shall be sealed at penetrations into the battery room to prevent hydrogen migration into other electrical equipment per NFPA 70.

The room or cabinet layout, including cell arrangement, charger and DC panel locations, working clearances, and ventilation routing, shall be as shown on the battery room layout.

VLA and vented Ni-Cd installations contain free liquid electrolyte and shall be provided with spill containment per IEEE 1578 and the applicable building and fire codes. The containment shall be sized to hold the volume of electrolyte from the largest single cell and shall be of materials compatible with the electrolyte.

For VLA installations, a built-up curb is the conventional method and provides the most reliable long-term containment. Modular containment trays integral to the rack are acceptable where the rack is so configured and the trays are listed for the electrolyte. A neutralization material (sodium bicarbonate for lead-acid sulfuric acid electrolyte; boric acid for Ni-Cd potassium hydroxide electrolyte) shall be stored adjacent to the battery in a clearly labeled container.

A spill kit appropriate to the chemistry shall be provided in the battery room. Eye-wash and emergency drench shower shall be provided where required by the applicable workplace safety code; the eye-wash shall be located within 10 seconds of unobstructed travel from any point in the battery work area.

The Contractor shall sequence the work so that the battery rack is installed and anchored, and the ventilation system is operational, before cells are placed on the rack. Cells shall not be left on a temporary surface or on the floor before installation, because handling damage to jars and posts is a common cause of premature cell failure.

The battery rack shall be assembled per the manufacturer's instructions on a level floor. Rack steel shall be electrically isolated from the cells by the manufacturer's supplied insulators; the rack itself shall be bonded to the building grounding electrode system per Grounding And BondingGrounding and Bonding for Electrical SystemsResolves to the current adopted revision.sync/grounding-and-bonding. Seismic anchorage shall be installed as shown on the seismic certification.

Cells shall be inspected on receipt for jar cracks, terminal damage, and shipping discharge below the manufacturer's threshold; cells outside the acceptable shipping voltage shall be set aside for the manufacturer's freshening charge before installation. Cells shall be installed in series order with consistent polarity per the cell numbering diagram, and intercell connectors shall be installed and torqued per the manufacturer's specification using a calibrated torque tool. Anti-corrosion compound shall be applied to the contact surfaces per the manufacturer's instructions.

After all cells are installed and connected, the total string voltage and the polarity at the battery main terminals shall be verified before the battery is connected to the charger.

Before the battery is placed in service, the Contractor shall apply the manufacturer's recommended initial charge or freshening charge. For VLA cells, this is conventionally an extended charge at the equalize voltage; for VRLA cells, this is typically a constant-current limited charge followed by a float period; for Ni-Cd cells, the initial charge follows the manufacturer's specific procedure for the plate construction. After the initial charge, the battery shall be allowed to stabilize at float for the manufacturer's recommended period before acceptance testing.

Working clearance at the battery, the charger, and the DC distribution panel shall comply with NFPA 70 Article 110.26 based on the system voltage. The aisle in front of the battery rack shall be at least 36 inches wide and shall accommodate the cell installation tool and the testing equipment.

Permanent, durable labels shall be applied to the battery, the charger, the DC distribution panel, and the battery disconnect, identifying:

• The system designation (e.g., "125 VDC Station Battery No. 1")
• The nominal voltage and the ampere-hour rating
• The chemistry and cell quantity
• The date of installation
• The connected load (at the charger and the DC panel)
• DC arc flash warning per NFPA 70E

A laminated single-line diagram of the DC system shall be posted at the DC distribution panel.

The cell manufacturer shall perform routine production tests on every cell, including capacity verification on a statistical sample basis, and shall provide a certificate of conformance for the cells supplied. Where witnessed factory testing of a complete battery is specified, the cells shall be assembled and discharged at the manufacturer's facility per IEEE 450 or the equivalent test for the chemistry.

The charger shall receive the manufacturer's standard production test, including output voltage and current verification, ripple measurement, and functional check of all alarms.

Contractor shall engage a qualified testing firm to perform acceptance testing per ANSI/NETA ATS and per IEEE 450 (VLA), IEEE 1188 (VRLA), or IEEE 1106 (Ni-Cd) as applicable to the chemistry. Testing shall occur after installation and initial charging are complete and before the battery is placed in service.

Field acceptance tests shall include as a minimum:

• Visual inspection of every cell, the rack, the intercell connectors, and the spill containment
• Measurement and recording of total float voltage and current
• Measurement and recording of individual cell or monobloc float voltage
• Measurement and recording of every intercell and intertier connection resistance, with comparison to the manufacturer's specified value and to the average of the string
• Measurement and recording of baseline internal resistance or conductance for each cell or monobloc, where the monitoring system or the cell manufacturer provides the equipment
• Ground continuity verification from the battery rack and the cabinet to the building grounding electrode system
• Charger functional test, including output voltage and ripple measurement, current limit verification, and operation of each alarm and indication
• Battery monitor functional test, including alarm and trend verification

A performance test or modified performance test at acceptance establishes the as-installed capacity of the battery and is the baseline against which all future performance is judged. IEEE 450, IEEE 1188, and IEEE 1106 each describe the corresponding test for their chemistries. The Engineer shall not waive the acceptance capacity test on the grounds of cost; a battery whose installed capacity was never measured cannot be defended at any later point in its life.

Any cell that fails the acceptance test, and any connection that fails the resistance check, shall be repaired or replaced and the affected portion of the battery shall be re-tested. The test report shall record both the initial result and the post-repair result.

The Contractor shall provide a recommended maintenance schedule and shall train the Owner's personnel in the periodic inspection and test procedures before substantial completion. The recommended schedule shall be keyed to the IEEE recommended practice for the chemistry: IEEE 450 for VLA, IEEE 1188 for VRLA, IEEE 1106 for Ni-Cd.

The following intervals are representative and shall be tailored to the installation by the Owner:

• Monthly — total float voltage, total float current (where measured), ambient temperature, visual inspection for leaks or unusual conditions, electrolyte level (VLA), pilot cell specific gravity (VLA)
• Quarterly — every cell float voltage, every cell temperature (or representative sample), connection resistance check on a rolling basis
• Annually — every cell internal resistance / conductance measurement, every intercell connection resistance, full visual inspection, electrolyte level top-up to specified level (VLA), pilot cell specific gravity (VLA), confirmation of charger float and equalize voltages, ventilation system functional check, ground continuity check, alarm function test
• Every 2 years (VRLA) or as recommended (other) — service test or performance test per the IEEE recommended practice
• Every 5 years and after any unusual event — full performance test per IEEE 450 / 1188 / 1106

A pilot cell shall be designated for VLA batteries; the pilot cell is the cell whose temperature and specific gravity are measured at the monthly interval as a representative of the string. The pilot cell shall be rotated periodically (typically annually) so that each cell is, over time, treated as the pilot.

The warranty for cells shall be from the cell manufacturer directly to the Owner, transferable from the Contractor at substantial completion. The prorated portion of the cell warranty is conventional in the industry and reflects the long published life of stationary cells; the Engineer shall confirm that the prorated terms are commercially reasonable and clearly stated before accepting the submittal.

Achieved capacity at the acceptance test shall be at least the manufacturer's published rated capacity adjusted for temperature; cells delivering less than 100 percent of rated capacity at acceptance shall be replaced by the manufacturer under warranty.

Spare cells, where provided, shall be stored on a level surface, kept in float charge or freshened on the manufacturer's recommended interval, and labeled with the installation-ready date. A spare cell that has been allowed to sit on the shelf for years without freshening is not a spare; it is a failed cell that the Owner does not yet know is failed.