Author: CHISEN Battery Team

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  OPzS2-250 2V250Ah Flooded Tubular Cell: Specs and String Sizing

  Answer First

The OPzS2-250 2V250Ah is a 2 V, 250 amp-hour flooded tubular vented lead-acid cell rated at the 10-hour rate — 25 A for 10 hours down to 1.80 V per cell at 20 °C — and it is the right cell for a telecom DC plant, a 108 V substation bus or a solar-and-storage cabinet that needs roughly 12 kWh nominal per 48 V string, on a site where a technician will still read the electrolyte level and top up distilled water every quarter.

It is not a sealed block. Hydrogen venting, acid-proof flame-retardant vent plugs, scheduled water top-up and periodic equalisation are part of the product, not optional extras. A project that treats the OPzS2-250 2V250Ah as a drop-in sealed cabinet battery discovers the difference in the first hot season.

The complete published data set sits on the OPzS2-250 2V250Ah model page, and the rest of the flooded range is listed under tubular flooded lead-acid batteries.

Key Takeaways

• Capacity is rate-dependent. The nameplate figure is 250 Ah at C10 (25 A to 1.80 V/cell at 20 °C). At longer rates the cell delivers more: 283 Ah at C24, 310 Ah at C48, 325 Ah at C72, 338 Ah at C100, 343 Ah at C120 and 350 Ah at C240 (Datasheet).
• Charging setpoints are fixed by the datasheet. Float 2.23 V/cell at 25 °C, equalising 2.35 V/cell at 25 °C, temperature compensation −3 mV/°C/cell, designed float life 20+ years at 20 °C (Datasheet). Solar and wind controllers use the 2.25 ± 0.005 V/cell float and 2.40 ± 0.01 V/cell equalising setpoints (Datasheet).
• Mechanical data is what decides the rack. Body 124 × 206 × 354 mm, 409 mm total height over the terminals, 15.5 kg without electrolyte and 20.5 kg with electrolyte, of which 5.0 kg is acid (Datasheet).
• Two limits protect the cell. Maximum charging current is 50 A (0.20 × C10) and internal resistance is about 0.88 mΩ fully charged at 20 °C, with a 2750 A short-circuit current (Datasheet).
• A 48 V string is simple arithmetic. 24 cells give 12,000 Wh nominal, 492.0 kg with electrolyte (24 × 20.5 kg) and 21.12 mΩ of internal resistance (24 × 0.88 mΩ) (Arithmetic).

§1 — OPzS2-250 2V250Ah Quick Specifications

Every row above is traceable. Values taken from the manufacturer’s OPzS2-250 datasheet are marked Datasheet, values taken from the published English product page are marked Model page, and derived figures are marked Arithmetic wherever they appear in the text. A supplier who cannot tell you which of the three a given figure is has not verified it.

Solar and wind controller setpoints for the OPzS2-250

Long-time discharge capacity for solar and wind duty (final voltage 1.85 V)

Source: Datasheet for the capacity row, Arithmetic for the energy row (2 V × Ah).

§2 — The Pain: Where 2V 250Ah Projects Go Wrong

The first failure is a specification failure. Buyers routinely receive a quotation that says only “2V 250Ah tubular” and treat every 2 V 250 Ah cell in the world as interchangeable. The published OPzS2-250 data makes the differences explicit: capacity at C10 is 250 Ah, but capacity at C24 is 283 Ah and at C240 is 350 Ah. A bank sized on the C10 number for a slow-discharge backup duty is undersized; a bank sized on the C240 number for a five-hour discharge duty is over-purchased. Both mistakes trace back to a quotation that never stated the rate and the end voltage.

The second failure is thermal. A 48 V string of 24 OPzS2-250 cells accepts a maximum charging current of 50 A per cell, so a charger set to deliver more — which happens when the charger is sized for the string’s nominal power rather than for the cells’ acceptance — pushes the electrolyte into gassing and dries the separator faster than the topping-up interval can repair. The same string on a solar site needs the higher 2.25 ± 0.005 V/cell float and the 2.40 ± 0.01 V/cell equalising setpoint; on a mains-float site the correct values are 2.23 V/cell and 2.35 V/cell at 25 °C. A controller left on the wrong setpoint is the classic cause of premature capacity loss.

The third failure is weight and access planning. The OPzS2-250 is 15.5 kg without electrolyte and 20.5 kg with electrolyte, and the full height over the terminals is 409 mm, not the 354 mm body height. A 24-cell string with electrolyte weighs 492.0 kg (24 × 20.5 kg, Arithmetic), and a 54-cell 108 V string weighs 1,107.0 kg (54 × 20.5 kg, Arithmetic). Cabinets, plinths, floor loading and lifting plans are usually drawn against the body height and a lighter shipping weight, and the result is a string that does not fit the rack and a handling plan that understates the load.

The fourth failure is assuming sealed behaviour. This cell vents hydrogen during overcharge, needs acid-proof flame-retardant vent plugs, needs distilled water, and needs a scheduled equalising period. Those four obligations are why the OPzS2-250 2V250Ah wins in cabinets with a permanent operator — a central DC plant serving a national mobile network operator in Chennai, a fixed-line exchange in Rotterdam, a substation compound outside Nairobi — and loses in unmanned roadside or container sites.

The fifth failure is ignoring parallel strings. A 48 V string of OPzS2-250 cells presents 21.12 mΩ of internal resistance (24 × 0.88 mΩ, Arithmetic). Two strings in parallel do not share load evenly once their float voltages separate by a few millivolts, and the weaker string silently carries less current while ageing faster. The cure is an equalising stage plus a rotation discipline, and both belong in the maintenance contract rather than in a commissioning checklist.

The delivery plan is part of the specification too. A 2 V 250 Ah vented article like this one leaves through Karachi and Santos for buyers in Pakistan and Brazil, and for importers moving stock through Mumbai, and the import file has to name the destination market before the container is booked rather than after it has sailed.

§3 — The Choice: The OPzS2-250 Against Its Published Siblings

Buyers comparing cells between 150 Ah and 350 Ah are choosing between three flooded capacities or between a flooded cell and a sealed one. The table below uses published values only.

Sources: OPzS2-150, OPzS2-250 and OPzS2-350 from their datasheets; OPzS2-200 from its datasheet; the comparison itself is Arithmetic.

Four numbers drive the decision. First, footprint. The 150 Ah and 200 Ah cells are 103 mm long; the 250 Ah and 350 Ah cells step up to 124 mm, while the width stays at 206 mm and the terminal spacing stays at 108 mm. A rack designed for the 103 mm cells does not accept the 124 mm cells without a new rail, and that is a change to the cabinet, the plinth and the cable entry.

Second, weight. Dry weight rises from 10.5 kg through 13.0 kg and 15.5 kg to 20.4 kg; wet weight rises from 14.5 kg through 17.5 kg and 20.5 kg to 27.0 kg. A cell that must be carried up a ladder or into a pit should be chosen with the wet weight in mind, not the dry one.

Third, internal resistance, which does not fall in a straight line with capacity at the bottom of the range — 1.2 mΩ at 150 Ah, 0.95 mΩ at 200 Ah, 0.88 mΩ at 250 Ah, 0.62 mΩ at 350 Ah — so a 24-cell string of the 350 Ah cell presents 14.88 mΩ (24 × 0.62 mΩ, Arithmetic) against 21.12 mΩ for the 250 Ah cell (24 × 0.88 mΩ, Arithmetic). The voltage drop under the same load is materially lower on the larger cell, which matters when the string is long and the load is heavy.

Fourth, the maintenance profile, and here the published data is unambiguous. The flooded OPzS2-250 carries 20.5 kg of electrolyte in an open container that must be topped up and periodically equalised, and 5.0 kg of acid per cell, so a 24-cell string carries 120.0 kg of acid (24 × 5.0 kg, Arithmetic) that has to be topped up and eventually replaced.

48 V string arithmetic across the flooded range

Source: Datasheet for the cell-level values, Arithmetic for the string rows.

For a 54-cell 108 V substation string the OPzS2-250 arithmetic gives a float bus of 120.42 V (54 × 2.23 V), 27,000 Wh nominal, 1,107.0 kg with electrolyte (54 × 20.5 kg), 47.52 mΩ of internal resistance (54 × 0.88 mΩ) and a 2,700 A maximum charging current (54 × 50 A) (Arithmetic).

Flooded against sealed at the 500 Ah step

Sources: OPzS2-500 and OPzV2-500 from their datasheets.

Two cells with the same 166 × 206 mm footprint and the same 500 Ah rating differ by 10.3 kg of weight (36.3 kg − 26.0 kg, Arithmetic), 36 mm of height (506 mm − 470 mm, Arithmetic), 0.06 mΩ of internal resistance, 20 A of charging acceptance and 1,100 A of short-circuit current — and one of them needs watering while the other does not. That is the whole flooded-versus-sealed decision expressed in published numbers, and it should be made on site-access economics rather than on the initial quotation.

If your string is larger than 350 Ah per cell, move to the OPzS flooded range overview rather than scaling the numbers in this table proportionally — plate thickness, internal volume and electrolyte quantity change non-linearly with capacity. The OPzV2-500 2V500Ah gel cell is the next published sealed step up.

§4 — The Framework: Seven Hard Checks Before You Sign

Q1. Match the charger to the cell’s acceptance, not to the string. The maximum charging current of the OPzS2-250 is 50 A (Datasheet). A 24-cell string therefore accepts at most 1,200 A (24 × 50 A, Arithmetic). Most telecom float rectifiers are sized well below that, which is correct; a solar controller set to the array’s full output is where the limit gets breached.

Q2. Apply temperature compensation to the setpoint, not to the battery. The published compensation is −3 mV/°C/cell on float (Datasheet), so a cell at 35 °C needs its 2.23 V/cell float reduced by 0.036 V. On a renewable site the published coefficient is −4 mV/cell/°C and the float setpoint is 2.25 ± 0.005 V/cell. Controllers that ignore this are permanently overcharging the string in the hot season and permanently undercharging it in winter.

Q3. Design for the float life at the site’s real temperature. The 20+ year design figure is quoted at 20 °C (Datasheet). A cabinet in Chennai, on a roof in Lagos or an outdoor enclosure in Durban will not deliver that figure, and the honest way to plan a replacement interval is to take the 20 °C number and treat every 10 °C of ambient uplift as a materially shorter service life.

Q4. Plan the watering interval from the real charging regime. A cell that is floated at 2.23 V/cell at 25 °C and never equalised loses water slowly; a cell that is equalised at 2.35 V/cell twice a month in a hot climate loses water fast enough to need attention on a monthly cycle. Put the interval in the maintenance contract, and put the electrolyte density check (1.240 g/cm³ at 20 °C, Datasheet) on the same schedule.

Q5. Size the interconnects and torque them correctly. The terminal is a female copper insert M8 with a published torque of 10–12 N·m (Datasheet). Under-torqued terminals generate heat at the joint; over-torqued ones damage the insert. The 2750 A short-circuit current (Datasheet) determines how quickly the fault must be cleared, and the cable cross-section is set by the string current rather than by the bolt size.

Q6. Decide how many strings run in parallel, and how they will be equalised. Two parallel strings will drift apart unless the charger has an equalising stage and the operator runs it. Parallel strings also multiply the water-top-up workload and the total string weight: 24 × 20.5 kg = 492.0 kg per 250 Ah string with electrolyte (Arithmetic), and 120.0 kg of acid per string (24 × 5.0 kg, Arithmetic).

Q7. Confirm the standards the cell is built to. A 2 V vented cell for stationary duty is normally specified against IEC 60896-11 and the equivalent DIN 40736 envelope, with IEC 61427 for the renewable cycling test, the Eurobat long life guide, BS 6290 part 4 and UL 1989 for the North American market. CHISEN production runs under ISO 9001 and ISO 14001 with GB/T 28001 occupational health and safety management, and the range is supplied with CE documentation, so the paperwork trail should exist before the first container is booked.

§5 — The Trust: What a Datasheet Must State — and What to Reject

The single most useful question a buyer can ask a supplier is: “which document is this number from?” A published datasheet answers five questions that quotations never answer. What is the capacity rate and the end voltage? For the OPzS2-250 it is 250 Ah at C10 to 1.80 V/cell at 20 °C, and the full curve to 240 hours is published alongside it. What is the weight with and without electrolyte? 15.5 kg and 20.5 kg — both numbers, because a shipping weight quoted without electrolyte tells you nothing about handling. What is the total height over the terminals? 409 mm, not the 354 mm body height, and the difference is exactly the kind of detail that stops a cabinet from being delivered. What is the maximum charging current? 50 A. What is the reference temperature for the internal resistance and for the float life? 20 °C for both, and both references matter more than the numbers themselves.

Against that standard, reject any quotation that quotes a float voltage above 2.23 V per cell for this model, or one that quotes a temperature compensation coefficient other than −3 mV/°C/cell, or one that quotes the 20+ year design life against 25 °C rather than 20 °C. The OPzS2-250 datasheet setpoints are 2.23 V/cell float, 2.35 V/cell equalising and −3 mV/°C/cell compensation, with the 20+ year design figure referenced to 20 °C. A supplier who quotes different numbers for the same model is either reading a different revision or inventing them.

Two further quality signals are worth checking on site. First, ask for the plant audit trail: paste mixing, grid casting, group assembly, formation and sealing are the process steps that decide whether a 250 Ah cell really holds 250 Ah in year five, and they are the difference between a manufacturer and a packer. Second, ask for the certification package — ISO 9001, ISO 14001, CE, UL and IEC documentation should arrive with the quotation, not three weeks after the deposit. CHISEN runs eight production bases with roughly 70 million kVAh of annual capacity, and the company profile is published on the CHISEN company page if you want to check the manufacturing scale behind a quotation before you commit a container.

§6 — FAQ

Q1. What is the rated capacity of the OPzS2-250 2V250Ah? 250 Ah at the 10-hour rate (25 A to 1.80 V/cell at 20 °C). The published table also gives 283 Ah at C24, 310 Ah at C48, 325 Ah at C72, 338 Ah at C100, 343 Ah at C120 and 350 Ah at C240 (Datasheet).

Q2. How many cells does a 48 V string need, and how much energy does it hold? 24 cells. 48 V × 250 Ah = 12,000 Wh nominal (Arithmetic). The string weighs 492.0 kg with electrolyte (24 × 20.5 kg) and 372.0 kg dry (24 × 15.5 kg), and carries 120.0 kg of acid (24 × 5.0 kg).

Q3. What float and equalising voltage should the charger use? Float 2.23 V/cell and equalising 2.35 V/cell, both referenced to 25 °C. On solar and wind sites use the higher 2.25 ± 0.005 V/cell float and 2.40 ± 0.01 V/cell equalising setpoint (Datasheet).

Q4. What temperature compensation does the cell need? −3 mV/°C/cell on float (Datasheet), applied to the setpoint. At 35 °C the float setpoint falls by 0.036 V per cell. Renewable controllers use the published −4 mV/cell/°C coefficient.

Q5. How long is the designed float life? 20+ years at 20 °C (Datasheet). Higher ambient temperatures reduce achievable service life, so site temperature has to be part of the replacement plan rather than a footnote.

Q6. What is the maximum charging current? 50 A per cell, which is 0.20 × C10 (Datasheet). For a 24-cell string the theoretical ceiling is 1,200 A (24 × 50 A, Arithmetic), and the charger should normally deliver far less.

Q7. Can this cell be installed without a permanent operator? It can be installed, but not forgotten. Flooded tubular cells need distilled-water top-up, electrolyte density checks, ventilation and periodic equalising. For an unmanned site, compare the published gel alternative instead.

Q8. What is the internal resistance and short-circuit current? About 0.88 mΩ fully charged at 20 °C (Datasheet) and a 2750 A short-circuit current (Datasheet). The string resistance of a 24-cell arrangement is 21.12 mΩ (24 × 0.88 mΩ, Arithmetic), and the 2750 A figure is what your DC fuse and disconnection arrangement must be able to interrupt.

Q9. How does the OPzS2-250 compare with the 150 Ah and 350 Ah cells? The 150 Ah and 200 Ah cells are 103 mm long; the 250 Ah and 350 Ah cells step up to 124 mm, with the width at 206 mm and terminal spacing at 108 mm throughout. Published differences are weight (15.5 kg dry and 20.5 kg wet against 10.5 kg and 14.5 kg for the 150 Ah cell, and 20.4 kg and 27.0 kg for the 350 Ah cell), charging limit (50 A against 30 A and 70 A), internal resistance (0.88 mΩ against 1.2 mΩ and 0.62 mΩ) and short-circuit current (2750 A against 2400 A and 3300 A). The OPzS2-250 2V250Ah model page carries the full data set.

Q10. Which standards and certifications apply? The flooded 2 V stationary cell is built to the IEC 60896-11 and DIN 40736 envelope, with IEC 61427 for renewable cycling, the Eurobat long life guide, BS 6290 part 4 and UL 1989 for the North American market. CHISEN supplies the range with CE documentation under ISO 9001 and ISO 14001 management systems, with GB/T 28001 occupational health and safety certification.

Expert Summary

The OPzS2-250 2V250Ah is a 2 V flooded tubular vented lead-acid cell with a published 250 Ah capacity at the 10-hour rate (25 A to 1.80 V/cell at 20 °C), rising to 350 Ah at the 240-hour rate; float 2.23 V/cell and equalising 2.35 V/cell at 25 °C with −3 mV/°C/cell compensation and a 20+ year design float life referenced to 20 °C; a body of 124 × 206 × 354 mm with 409 mm total height over the terminals; a weight of 15.5 kg without electrolyte and 20.5 kg with electrolyte, of which 5.0 kg is acid; a 50 A maximum charging current; about 0.88 mΩ internal resistance at 20 °C; and a 2750 A short-circuit current. A 24-cell 48 V string of these cells holds 12,000 Wh nominal, weighs 492.0 kg with electrolyte and presents 21.12 mΩ of internal resistance; a 54-cell 108 V string floats at 120.42 V, holds 27,000 Wh and weighs 1,107.0 kg. The cell is the correct choice where a manned telecom DC plant, substation or renewable cabinet benefits from long float life and low cost per usable year; where site access is unattended, the published gel alternative trades a slightly different internal resistance and charging limit for the removal of the watering cycle.

Contact CHISEN — 24-Hour Response

If you are quoting a 2 V 250 Ah cell for a 48 V DC plant, a 108 V substation in Rotterdam or a solar cabinet outside Nairobi, ask for the complete OPzS2-250 datasheet, the string layout drawing and the certification package, and ask for them in writing: email sales@chisen.cn, or message the export desk on WhatsApp at +86 131 6622 6999 (https://wa.me/8613166226999). One line describing your bus voltage, backup time and site temperature is enough for us to return the string arithmetic, the charger setpoints and the nearest capacity in the flooded range — or the gel equivalent if nobody will ever top up water on that site.

Browse the full CHISEN lead-acid range and technical data at https://leadacidbattery.cn.

Related CHISEN Product Pages

• OPzS2-250 2V250Ah model page — full published specification set
• OPzS2-350 2V350Ah tubular flooded cell — the next capacity step, 350 Ah
• Tubular flooded battery range — 2 V cells from 100 Ah to 3,000 Ah