Introduction
An international buyer sends an RFQ:
2V 1000Ah OPzV Battery – 108 pcs. Please quote.
At first glance, the requirement appears clear.
It is not.
Two manufacturers can both offer a product labeled:
2V 1000Ah OPzV
yet the actual project performance can differ because the RFQ did not specify:
- Capacity rating time
- Final voltage
- Rating temperature
- Standby or cycling duty
- Required autonomy
- Charging parameters
- Applicable standard
- Acceptance test
- Design-life conditions
This is one of the most common causes of technical disagreement between:
- Battery supplier
- EPC contractor
- Distributor
- End user
A good battery tender should define the required performance, not merely the label.
1. Specify OPzV or OPzS Clearly
The first requirement should state the battery construction.
OPzV
Typically:
- 2V tubular positive plate
- Gelled electrolyte
- Valve-regulated construction
- Low routine water maintenance
OPzS
Typically:
- 2V tubular positive plate
- Flooded liquid electrolyte
- Vented construction
- Requires electrolyte-level maintenance
The site’s existing OPzV/OPzS comparison explains this fundamental construction difference.
Do not write only:
“Tubular battery.”
That is not sufficiently specific.
2. Nominal Capacity Must Include the Rating Condition
Instead of:
2V 1000Ah
write something similar to:
Required nominal capacity: 1000Ah at the specified discharge rate, final voltage, and reference temperature.
The actual numerical conditions should come from the project requirement.
Common stationary ratings may use:
- C10
- 8-hour rate
- Other specified durations
For example, EnerSys lists OPzV capacity according to defined C10 and end-voltage/temperature conditions, illustrating why capacity cannot be separated from the test conditions.
3. Specify End-of-Discharge Voltage
This is essential.
Suppose Supplier A quotes capacity to:
1.80 V/cell
and Supplier B uses:
1.75 V/cell
The two Ah figures are not directly equivalent.
A lower final voltage allows more capacity to be extracted.
Therefore, the RFQ should state:
- Discharge duration
- Final voltage per cell
- Total final DC bus voltage, if relevant
This also allows the supplier to confirm that the critical DC equipment can continue operating at end of discharge.
4. State the Reference Temperature
Battery capacity changes with temperature.
A battery rated at:
20°C
should not automatically be expected to deliver identical capacity at:
5°C
EnerSys OPzV instructions show significant capacity reduction at lower battery temperatures, with explicit correction factors used for performance evaluation.
The tender should define:
- Rating temperature
- Actual site temperature
- Minimum expected battery-room temperature
- Maximum expected temperature
This is particularly important for projects in:
- Middle East
- Africa
- Northern Europe
- High-altitude regions
5. Define Standby Duty or Cycling Duty
This can completely change the appropriate battery specification.
Standby Applications
Examples:
- Substations
- UPS systems
- Emergency DC systems
The battery remains on float most of the time and discharges occasionally.
Cycling Applications
Examples:
- Off-grid solar
- Hybrid power
- Renewable-energy storage
The battery may discharge daily.
The same “2V 1000Ah” label does not tell the supplier which duty is required.
IEC 60896-21 and IEC 60896-22 apply to stationary VRLA batteries for float-charge standby applications, including telecom, UPS, utility switching and emergency power.
Importantly, IEC 60896-21 explicitly excludes photovoltaic battery applications from its scope.
For photovoltaic off-grid applications, IEC 61427-1 addresses batteries used in off-grid PV energy storage.
For on-grid renewable-energy storage, IEC 61427-2 covers performance and endurance testing for secondary batteries used in grid-connected EES applications, with the consolidated version incorporating Amendment 1:2024.
This distinction is valuable when writing tenders.
6. Select the Applicable Standard Correctly
A strong RFQ should not simply write:
“IEC standard required.”
State which standard is relevant.
OPzV – Stationary VRLA Standby Applications
Relevant examples include:
- IEC 60896-21: test methods
- IEC 60896-22: requirements
These standards apply to valve-regulated stationary lead-acid batteries used in float-charge applications.
OPzS – Vented Stationary Applications
IEC 60896-11 applies to vented stationary lead-acid batteries.
Renewable-Energy Applications
Depending on the project:
- IEC 61427-1: photovoltaic off-grid
- IEC 61427-2: on-grid renewable-energy storage
Using the correct standard improves technical comparability between suppliers.
7. Do Not Mix “Design Life” and “Warranty”
These terms are often confused.
A supplier may state:
Design life: 20 years
This does not mean:
20-year warranty.
Design life is normally based on defined operating conditions such as:
- Temperature
- Float voltage
- Duty
- Maintenance
Warranty is a commercial obligation governed by:
- Warranty period
- Conditions
- Exclusions
- Claim procedure
A good RFQ should request both separately.
8. Define the Required Backup Time
Instead of buying batteries only by Ah, specify the actual duty.
For example:
- Continuous DC load: X amps
- Backup duration: Y hours
- Final DC voltage: Z volts
For more complex substations, provide a load profile including:
- Continuous load
- Short-duration trip load
- Closing current
- Emergency loads
Then the supplier can select capacity from the appropriate discharge table.
9. Include Peak Current Requirements
This is particularly important for:
- Switchgear
- Telecom
- UPS
- Industrial DC systems
A battery may have enough Ah but still experience excessive voltage sag under high peak current.
Tender documents should identify:
- Maximum short-duration current
- Duration
- Required minimum DC voltage during the event
This prevents selecting batteries based on energy capacity alone.
10. State the Required Number of Cells Carefully
For a 110V or 220V system, do not specify cell count blindly.
Provide:
- Nominal DC voltage
- Maximum permitted DC voltage
- Minimum equipment operating voltage
- Charger voltage range
This allows cell count to be checked against:
- Maximum float/boost voltage
- End-of-discharge voltage
A 110V DC system is not automatically defined only by “55 × 2V cells.”
11. Specify Charging Requirements
The tender should request manufacturer-recommended:
- Float voltage
- Boost/absorption voltage
- Charging-current limit
- Temperature compensation
For OPzS, also define whether equalization is expected.
For OPzV, avoid automatically applying an OPzS flooded-battery equalization requirement.
EnerSys OPzV instructions, for example, specify product-specific float, boost and charging-current requirements.
12. Clarify Parallel-String Design
If additional Ah is achieved using multiple strings, specify:
- Number of parallel strings
- Individual string protection
- Equal cable length
- Equal cable cross-section
EnerSys OPzV instructions recommend batteries of the same capacity, design and age for parallel strings and specify equal cable resistance between strings.
Avoid creating a tender that permits unlimited parallel strings simply to reach the required Ah.
13. Define the Battery Rack Requirement
Do not treat racks as an afterthought.
Specify:
- Number of tiers
- Number of rows
- Seismic requirement if applicable
- Corrosion protection
- Battery-room dimensions
- Maintenance clearance
For OPzS installations, consider access for:
- Electrolyte inspection
- Water topping-up
- Hydrometer testing
For OPzV, access is still required for:
- Voltage measurement
- Resistance testing
- Replacement
14. Include Intercell Connectors and Hardware
Clarify whether the battery price includes:
- Intercell connectors
- Bolts
- Washers
- Terminal covers
- Rack
- Flexible connectors
A low battery quotation may exclude accessories required to assemble the actual bank.
15. Define Acceptance Testing
This is one of the most important tender sections.
Ask whether the project requires:
Factory Testing
Examples:
- Capacity verification
- Voltage inspection
- Internal resistance
- Dimensional inspection
Site Acceptance Testing
Examples:
- Individual cell voltage
- Total string voltage
- Connection resistance
- Capacity/autonomy test
Define:
- Test current
- Final voltage
- Temperature correction
- Acceptance percentage
before placing the order.
Do not wait until after installation to decide how the batteries will be judged.
16. Request Baseline Data
For large projects, baseline information is valuable for future maintenance.
Request or record at commissioning:
- Individual cell voltage
- Internal resistance/impedance
- Terminal connection resistance
- Battery temperature
EnerSys OPzV maintenance instructions specifically recommend maintaining records including connection resistance, temperature and operational events.
Without baseline data, five-year maintenance decisions become much harder.
17. Specify Documentation Requirements
A professional RFQ may request:
- Technical data sheet
- Installation manual
- Charging instructions
- Maintenance manual
- Test report
- Certificate of conformity
- IEC compliance documentation
- Factory inspection report
- Packing list
- Country of origin
For OPzS projects, also consider:
- Electrolyte specification
- Filling instructions
- Water-quality requirements
18. Define Shipment Condition for OPzS
This is important for international projects.
OPzS may be supplied:
- Filled and charged
- Moist charged
- Dry charged
The RFQ should state the required arrangement.
If dry charged, clarify:
- Is electrolyte included?
- Who will supply acid locally?
- Who will perform activation?
- What commissioning support is required?
Otherwise the batteries may arrive on site with no practical activation plan.
19. Specify Terminal and Layout Requirements
For replacement projects, request:
- Terminal position
- Polarity orientation
- Cell dimensions
A replacement battery that does not fit the existing rack can create substantial site modifications.
Photographs and drawings of the existing installation should be sent to the supplier.
20. Include Environmental Conditions
Provide:
- Indoor/outdoor installation
- Ventilation
- Maximum temperature
- Minimum temperature
- Humidity
- Altitude
- Dust conditions
A battery supplier cannot properly evaluate a project using only Ah capacity.
21. Ask for Weight—But Do Not Use Weight as the Only Quality Measure
Weight can provide useful information when comparing very similar battery designs because lead content contributes substantially to product mass.
However:
heavier does not automatically mean better.
Performance should be compared using:
- Capacity
- Discharge curves
- Cycle data
- Standards
- Construction
- Test documentation
Do not reject or approve a supplier using kilograms alone.
A Better RFQ Example
Instead of:
2V 1000Ah OPzV — 108 pcs
use a requirement structure such as:
Battery Type: 2V OPzV tubular GEL stationary battery
Application: Substation DC backup
Nominal DC System: ___ VDC
Required Capacity: ___ Ah at ___-hour rate
Final Voltage: ___ V/cell
Reference Temperature: ___ °C
Required Backup Time: ___ hours
Continuous Load: ___ A
Peak Load: ___ A for ___ seconds
Applicable Standard: ___
Battery Quantity: ___ cells
Required Rack: Yes / No
Acceptance Test: ___
Installation Temperature: ___ °C
Required Documents: ___
This allows suppliers to quote against the same technical basis.
OPzV Tender Standard Selection Example
For a conventional stationary telecom or UPS float application, IEC 60896-21/22 may be relevant to the VRLA battery testing and requirements.
For an off-grid solar project, however, specifying only IEC 60896-21 may be inappropriate because its scope excludes photovoltaic battery applications; IEC 61427-1 specifically addresses batteries for photovoltaic off-grid use.
This is exactly the kind of detail that prevents a tender from looking technically complete while actually specifying the wrong test basis.
OPzS Tender Standard Selection Example
For stationary vented OPzS batteries, IEC 60896-11 applies to vented lead-acid batteries designed for fixed stationary service.
If the OPzS bank will cycle in a renewable-energy system, also evaluate the relevant renewable-energy battery duty and testing requirements rather than treating the project as pure float standby.
Common RFQ Mistakes
“2V 1000Ah” with No C-Rate
Supplier quotations cannot be compared correctly.
No End Voltage
Different manufacturers may use different discharge endpoints.
No Temperature
Cold-climate capacity requirements may be underestimated.
“20-Year Life Required” with No Operating Conditions
Life claims are meaningless without temperature and duty.
“IEC Required” Without Standard Number
Different standards apply to different battery types and applications.
No Acceptance-Test Procedure
Capacity disputes arise after installation.
No Charging Requirements
Existing charger may be incompatible.
No Project Load Profile
Battery may be oversized or undersized.
Frequently Asked Questions
Is 2V 1000Ah enough information for an OPzV quotation?
It is enough for an initial price indication, but not enough for a reliable project design or fair technical comparison.
Which IEC standard applies to OPzV?
IEC 60896-21 and -22 cover stationary VRLA batteries for float-charge standby applications. Renewable-energy projects may require IEC 61427 standards depending on the application.
Which IEC standard applies to OPzS?
IEC 60896-11 applies to stationary vented lead-acid batteries.
Should the RFQ specify C10?
If C10 is the project’s required capacity basis, yes. Always state the discharge duration, final voltage and reference temperature together.
Should warranty and design life be written separately?
Yes. They are not the same concept.
What information should a distributor send before requesting a quotation?
At minimum: battery type, system voltage, required capacity, application, backup time, temperature, charger information, quantity and applicable project standards.
Conclusion
The biggest mistake in OPzV and OPzS procurement is buying a battery label instead of specifying a battery duty.
A strong tender should define:
battery technology + capacity rate + final voltage + temperature + load + autonomy + charging + standards + testing + installation requirements.
This makes supplier quotations easier to compare and significantly reduces disputes after installation.
For distributors and EPC contractors, providing these parameters at the RFQ stage also allows the battery manufacturer to recommend the correct:
- Cell size
- Cell quantity
- Charger settings
- Battery rack
- Testing procedure
instead of simply quoting the cheapest product labeled “2V 1000Ah.”
