OPzS2-350 2V350Ah Flooded Tubular Cell: Specs and String Sizing

Answer First

The OPzS2-350 2V350Ah is a 2 V, 350 amp-hour flooded tubular vented lead-acid cell rated at the 10-hour rate — 35 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 or 216 V substation bus, or a utility-scale solar-and-storage container that needs roughly 16.8 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 OPzS2-350 2V350Ah as a drop-in sealed cabinet battery discovers the difference in the first hot season.

The complete published data set sits on the OPzS2-350 2V350Ah 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 350 Ah at C10 (35 A to 1.80 V/cell at 20 °C). At longer rates the cell delivers more: 396 Ah at C24, 434 Ah at C48, 455 Ah at C72, 473 Ah at C100, 480 Ah at C120 and 490 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 × 471 mm, 525 mm total height over the terminals, 20.4 kg without electrolyte and 27.0 kg with electrolyte, of which 6.6 kg is acid (Datasheet).
• Two limits protect the cell. Maximum charging current is 70 A (0.20 × C10) and internal resistance is about 0.62 mΩ fully charged at 20 °C, with a 3300 A short-circuit current (Datasheet).
• A 48 V string is simple arithmetic. 24 cells give 16,800 Wh nominal, 648.0 kg with electrolyte (24 × 27.0 kg) and 14.88 mΩ of internal resistance (24 × 0.62 mΩ) (Arithmetic).

§1 — OPzS2-350 2V350Ah Quick Specifications

Every row above is traceable. Values taken from the manufacturer’s OPzS2-350 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 OPzS2-350

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 350Ah Projects Go Wrong

The first failure is a specification failure. Buyers routinely receive a quotation that says only “2V 350Ah tubular” and treat every 2 V 350 Ah cell in the world as interchangeable. The published OPzS2-350 data makes the differences explicit: capacity at C10 is 350 Ah, but capacity at C24 is 396 Ah and at C240 is 490 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 OPzS2-350 cells accepts a maximum charging current of 70 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, and at 350 Ah it becomes the dominant issue. The OPzS2-350 is 20.4 kg without electrolyte and 27.0 kg with electrolyte, and the full height over the terminals is 525 mm, not the 471 mm body height. A 24-cell string with electrolyte weighs 648.0 kg (24 × 27.0 kg, Arithmetic), and a 54-cell 108 V string weighs 1,458.0 kg (54 × 27.0 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 OPzS2-350 2V350Ah 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 same OPzS2-350 2V350Ah moves out of Hamburg and Antwerp for European utility buyers and into Valencia and other ports in Spain for Mediterranean projects, so the destination market belongs in the enquiry rather than in the shipping stage.

The fifth failure is ignoring parallel strings. A 48 V string of OPzS2-350 cells presents 14.88 mΩ of internal resistance (24 × 0.62 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.

§3 — The Choice: The OPzS2-350 Against Its Published Siblings

Buyers comparing cells between 250 Ah and 420 Ah are choosing between two flooded capacities and, increasingly, between a flooded and a sealed cell of the same rating. The table below uses published values only.

Sources: OPzS2-250 and OPzS2-350 from their datasheets; OPzS2-420 and OPzV2-420 from their published specification pages and datasheets; the comparison itself is Arithmetic.

Four numbers drive the decision. First, footprint and height. The 250 Ah cell is 124 × 206 × 354 mm with a 409 mm total height; the 350 Ah cell keeps the same 124 × 206 mm footprint but grows to 471 mm of body and 525 mm total height. The 420 Ah cell then steps the length up to 145 mm. A rack designed for the 350 Ah cell will not accept the 420 Ah cell without a new rail, and a room designed for a 409 mm cell will not accept a 525 mm cell without rebuilding the plinth.

Second, weight. Dry weight rises from 15.5 kg to 20.4 kg and 24.0 kg; wet weight rises from 20.5 kg to 27.0 kg and 32.0 kg. At 350 Ah a cell that must be carried up a ladder or into a pit should be chosen with the 27.0 kg wet weight in mind, not the 20.4 kg dry one.

Third, internal resistance. 0.88 mΩ at 250 Ah, 0.62 mΩ at 350 Ah and 0.56 mΩ at 420 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) and 13.44 mΩ for the 420 Ah cell (24 × 0.56 mΩ, Arithmetic). The voltage drop under the same load falls as capacity rises, which matters when the string is long and the load is heavy.

Fourth, the maintenance profile, and this is where the flooded-versus-sealed decision becomes concrete. The flooded OPzS2-350 carries 27.0 kg of electrolyte and 6.6 kg of acid per cell, so a 24-cell string carries 158.4 kg of acid (24 × 6.6 kg, Arithmetic) that must be topped up and eventually replaced. The gel OPzV2-420 carries the same 145 × 206 × 471 mm body at 31.5 kg with a 506 mm total height, needs no watering, and may be installed horizontally — at a higher internal resistance of 0.62 mΩ against 0.56 mΩ for the flooded cell of the same rating.

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 OPzS2-350 arithmetic gives a float bus of 120.42 V (54 × 2.23 V), 37,800 Wh nominal, 1,458.0 kg with electrolyte (54 × 27.0 kg), 33.48 mΩ of internal resistance (54 × 0.62 mΩ) and a 3,780 A maximum charging current (54 × 70 A) (Arithmetic). On a 216 V three-phase DC bus the string becomes 108 cells, giving a float bus of 240.84 V (108 × 2.23 V), 75,600 Wh nominal and 2,916.0 kg with electrolyte (108 × 27.0 kg, Arithmetic).

If your string is larger than 420 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 OPzS2-500 2V500Ah cell is the next published step up, at 166 × 206 × 470 mm and 26.0 kg with electrolyte.

§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 OPzS2-350 is 70 A (Datasheet). A 24-cell string therefore accepts at most 1,680 A (24 × 70 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 3300 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 × 27.0 kg = 648.0 kg per 350 Ah string with electrolyte (Arithmetic), and 158.4 kg of acid per string (24 × 6.6 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 OPzS2-350 it is 350 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? 20.4 kg and 27.0 kg — both numbers, because a shipping weight quoted without electrolyte tells you nothing about handling. What is the total height over the terminals? 525 mm, not the 471 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? 70 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 OPzS2-350 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 350 Ah cell really holds 350 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.

§6 — FAQ

Q1. What is the rated capacity of the OPzS2-350 2V350Ah? 350 Ah at the 10-hour rate (35 A to 1.80 V/cell at 20 °C). The published table also gives 396 Ah at C24, 434 Ah at C48, 455 Ah at C72, 473 Ah at C100, 480 Ah at C120 and 490 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 × 350 Ah = 16,800 Wh nominal (Arithmetic). The string weighs 648.0 kg with electrolyte (24 × 27.0 kg) and 489.6 kg dry (24 × 20.4 kg), and carries 158.4 kg of acid (24 × 6.6 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? 70 A per cell, which is 0.20 × C10 (Datasheet). For a 24-cell string the theoretical ceiling is 1,680 A (24 × 70 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 0.62 mΩ fully charged at 20 °C (Datasheet) and a 3300 A short-circuit current (Datasheet). The string resistance of a 24-cell arrangement is 14.88 mΩ (24 × 0.62 mΩ, Arithmetic), and the 3300 A figure is what your DC fuse and disconnection arrangement must be able to interrupt.

Q9. How does the OPzS2-350 compare with the 250 Ah and 420 Ah cells? The 250 Ah cell is 124 × 206 × 354 mm with a 409 mm total height; the 350 Ah cell keeps the 124 × 206 mm footprint but grows to 471 mm of body and 525 mm total height; the 420 Ah cell steps the length up to 145 mm. Published differences are weight (20.4 kg dry and 27.0 kg wet against 15.5 kg and 20.5 kg for the 250 Ah cell, and 24.0 kg and 32.0 kg for the 420 Ah cell), charging limit (70 A against 50 A and 84 A), internal resistance (0.62 mΩ against 0.88 mΩ and 0.56 mΩ) and short-circuit current (3300 A against 2750 A and 3500 A). The OPzS2-350 2V350Ah 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 OPzS2-350 2V350Ah is a 2 V flooded tubular vented lead-acid cell with a published 350 Ah capacity at the 10-hour rate (35 A to 1.80 V/cell at 20 °C), rising to 490 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 × 471 mm with 525 mm total height over the terminals; a weight of 20.4 kg without electrolyte and 27.0 kg with electrolyte, of which 6.6 kg is acid; a 70 A maximum charging current; about 0.62 mΩ internal resistance at 20 °C; and a 3300 A short-circuit current. A 24-cell 48 V string holds 16,800 Wh nominal, weighs 648.0 kg with electrolyte and presents 14.88 mΩ of internal resistance; a 54-cell 108 V string floats at 120.42 V, holds 37,800 Wh and weighs 1,458.0 kg. The cell suits a manned telecom DC plant, substation or utility-scale storage container; where access is unattended, the published gel alternative trades a different internal resistance and installation orientation for the removal of the watering cycle.

Contact CHISEN — 24-Hour Response

If you are quoting a 2 V 350 Ah cell for a 48 V DC plant, a 108 V substation in Rotterdam or a storage container outside Nairobi, ask for the complete OPzS2-350 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

• OPzS2-350 2V350Ah model page — full published specification set
• OPzS2-420 2V420Ah tubular flooded cell — the next capacity step, 420 Ah
• Tubular flooded battery range — 2 V cells from 100 Ah to 3,000 Ah

CHISEN Battery Team

Engineering and export team at CHISEN Battery, Hangzhou, China. Lead-acid and lithium battery manufacturer, ISO 9001 / CE / UL certified, exporting to 50+ countries.

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