Category: Battery Knowledge

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  OPzS2-770 2V770Ah Tubular Battery: DC Plant Sizing Guide

Reading time: 20 minutes | For: telecom power engineers, DC panel and data-centre engineers, solar EPC contractors, railway signalling engineers, industrial power distributors and OEM buyers across Africa, the Middle East, South Asia, South-East Asia and Latin America

Answer First

The OPzS2-770 2V770Ah is a 2-volt, 770 amp-hour stationary battery cell built on a tubular positive plate with liquid dilute-sulphuric-acid electrolyte in a vented, transparent-container case, constructed to DIN 40736-1 and IEC 60896-11. It is the flooded workhorse of the stationary lead-acid world — the cell you specify when the site has a staffed room, a maintenance route, and a duty cycle that rewards deep cycling over pure float standby.

Five numbers decide the procurement:

• 770Ah at the 10-hour rate (C10) to 1.80 V per cell — one cell, six bus voltages: 24 cells = 48V, 54 cells = 108V (110V DC panel), 108 cells = 216V (220V industrial), 190 cells = 380V three-phase DC.
• 254 × 210 × 471 mm, 525 mm total height — a transparent SAN container, so you can see the electrolyte level and plate condition from the aisle. No infrared camera, no guesswork.
• 1,500–2,500 cycles at 80% depth of discharge — roughly 1.5–2× the cycle life of a flat-plate AGM at the same amp-hour rating, because the tubular plate holds active material mechanically instead of relying on a corroding grid.
• 3,900 A short-circuit current and 0.55 mΩ internal resistance fully charged at 25°C, giving better voltage retention under the high-rate pulses a DC panel or a railway signalling supply actually produces.
• 20–25 years of float design life at 25°C — and that figure halves for every 10°C rise in ambient, which makes room design a battery-life decision rather than a facilities decision.

The honest caveat: the OPzS is not maintenance-free. It needs a water top-up every 3–6 months and must be installed upright. If your site is unmanned, remote, or in a sealed container where nobody will ever walk past the rack, the sealed tubular gel OPzV is usually the lower total-cost answer despite the higher purchase price. That trade-off is the whole decision, and §3 quantifies it over ten years.

Key Takeaways

1. OPzS2-770 = 2V cell, 770Ah at C10, 254 × 210 × 471 mm (525 mm total height), Φ20-M8 terminal, flooded tubular plate, SG 1.24 electrolyte. Published figures.
2. One cell, six bus voltages. 24 cells = 48V, 30 = 60V, 54 = 108V, 108 = 216V, 190 = 380V. Write the cell count into the purchase order, not just the bus voltage.
3. Tubular plate beats flat plate on cycle life, and loses on footprint. 1,500–2,500 cycles at 80% DOD versus roughly 500–1,000 for flat-plate AGM — but a 770Ah tubular cell occupies more floor area per kWh than an AGM block of the same capacity.
4. Capacity derates hard above 35°C. Float life halves for every 10°C rise (Arrhenius): 25°C ≈ 20–25 years, 35°C ≈ 10–12 years, 45°C ≈ 5–6 years.
5. Sizing is almost always done on the wrong discharge rate. The same cell rated 770Ah at C10 delivers roughly 660Ah at C3. Specify the rate your application actually runs at.
6. CHISEN supplies factory-direct with 8 production bases, 70 GWh annual capacity, CE / ISO 9001 / ISO 14001 / UL / IEC certification, and export documentation prepared for 60+ destination markets including SONCAP, PVOC, SASO, BIS and ESMA on request.

§1 — The Published Specification Table

Two data-integrity flags you should know about before you order. We would rather tell you this than have you discover it at the loading dock. On the currently published model page for the OPzS2-770, two fields are inconsistent with a 770Ah cell:

• The discharge-rate table is copied from a much smaller cell. It lists 1 HR at 50 Ah, 3 HR at 75 Ah, 10 HR at 100 Ah and 240 HR at 130 Ah — values in the range of a 100Ah cell, not a 770Ah cell. For a genuine 770Ah cell those figures should be roughly 7.7 times higher.
• The weight field is not consistently published. A figure in the region of 12.6 kg appears in the page content, which belongs to a far smaller case; a 770Ah tubular cell of this size is several times that.

We are not going to reproduce either number as if it were correct. Instead: request the current datasheet with your quotation and confirm the weight, the discharge table and the terminal option against it before you release the order. Template-copy errors of this kind are common across model pages in this industry, and the ten-minute check protects a bank that costs several thousand dollars. The verified figures in the table above — capacity, dimensions, terminal type, internal resistance, short-circuit current, cycle life, float life and standards — are the ones we stand behind.

What “OPzS2-770” tells you. OPz identifies the tubular-plate stationary range. S denotes flooded, vented construction, as opposed to V for valve-regulated gel. The 2 is the cell voltage. 770 is the amp-hour rating at the ten-hour rate. In the DIN 40736-1 convention, the number following the letter pair is always the ten-hour rate, which is why the rating is directly comparable across the whole OPz range.

String configuration reference.

Individual model pages confirm the variant: OPzS2-770 2V770Ah specifications →. For the full flooded tubular range, see the OPzS tubular flooded battery series →.

§2 — The Pain: Where Stationary Projects Actually Lose Their Budget

The room nobody walks into. The single largest cost surprise in stationary lead-acid is the battery room itself. A flooded installation needs ventilation for hydrogen, a floor with drainage and acid resistance, a maintenance route, lighting, and — critically — someone who actually visits. When a project is built and then handed to an operator with no routine maintenance, a flooded bank specified for a 20-year design life delivers five.

Temperature is the number nobody put in the specification. Float life follows the Arrhenius rule: every 10°C rise roughly halves float life. A 20-year-plus cell installed in a 45 °C unventilated container room delivers roughly five years. No chemistry fixes this; only thermal design does. And in Nairobi, Lagos, Karachi, Chennai, Dubai, Manila and Jakarta, indoor ambient frequently sits above 35°C for most of the year.

Note the second row carefully: above 25°C a lead-acid cell delivers more than its rated capacity at a low discharge rate, which is a genuine bonus for a telecom site — but it buys no extra calendar life, because heat accelerates the ageing chemistry faster than it increases capacity.

Sizing on the wrong discharge rate. 770Ah is the ten-hour rate rating. At the three-hour rate the same cell delivers roughly 660Ah, and at the one-hour rate roughly 570Ah. A DC panel sized for a deep discharge event but quoted at C10 will be under-specified by 15–20% on the worst event of its life — which is precisely the event the system exists to survive.

The 48V string is not a 48V string. Every cell in a series string carries the full bus voltage, and the string’s usable capacity is limited by its weakest cell. A 24-cell string with one cell at 1.95V open circuit imposes 46.8V across the bus, not 48V. Cell-to-cell imbalance — not a dead cell — is what actually ends strings early.

§3 — The Choice: Flooded Tubular vs Sealed Gel vs Lithium, Quantified

The table below models a realistic duty: one 48V telecom DC plant or small data-centre site, 24 × OPzS2-770 cells, float standby with periodic discharge events, 30°C average ambient, ten-year horizon. All figures are a stated-assumption model so you can rebuild it with your own tariff, labour rate and duty profile — not a quotation.

Read the third row down. The labour line is the whole argument. Flooded tubular loses $2,080 over ten years to watering and inspection visits, and a further $2,880 to one mid-life replacement. Those two lines together are the entire gap to the sealed gel option, which costs more per cell and less in total.

Where the conclusion changes:

• Flooded OPzS wins where the site has a staffed maintenance route, a water supply and a proper ventilated battery room — because it is the lowest-cost product by a wide margin and its cycle life is the highest in the comparison. If a technician already visits the site monthly, flooded is the right answer.
• Sealed tubular gel OPzV wins at unmanned, remote and containerised sites: same tubular plate cycle-life advantage, no watering route, and installation in any orientation except inverted. It is the most common correct answer for telecom base stations and remote solar sites.
• Lithium wins over a ten-year horizon in this model, but with two conditions attached: the capital must be available, and the cells must carry the listing your destination requires. Some telecom and utility operators are bound by UL 1973, UL 9540A or equivalent national approvals where lead-acid passes more easily. Confirm before committing.
• Lithium’s advantage disappears if your horizon is short. At five years the numbers are much closer, and if the site has a maintenance route, flooded or gel lead-acid usually wins.

The same model, if the site is manned and warm. Flooded’s disadvantage is labour that already exists. Where a technician’s monthly visit is already on the schedule for other reasons, the labour line shrinks toward $400 and the ten-year totals converge to roughly $9,150 flooded, $9,500 gel and $8,090 lithium. At that point the decision is about cycle life, footprint and process discipline rather than cost.

§4 — The Framework: Seven Criteria Before You Issue a Purchase Order

1. Establish the discharge profile, then the rate you will size at. DC plant duty is float with occasional deep discharge. Size for the worst event at the rate the event actually occurs, then apply the end-voltage table in §5. Do not size on the C10 nameplate for a deep event.

2. Fix the cell count explicitly. 24 cells = 48V, 30 = 60V, 54 = 108V, 108 = 216V, 190 = 380V. Write “24 × OPzS2-770, 48V” on the order. A 48V string built from 24 two-volt cells and a 48V string built from a different cell count are not the same battery, and mixing them across a site is how string imbalance starts.

3. Design the room before the cells arrive. Ventilation for hydrogen, drainage and an acid-resistant floor, lighting, a maintenance route, and a working clearance of at least 50 mm behind each string. Check the rack against the cell drawing — 254 × 210 mm on a 525 mm tall cell with a Φ20-M8 terminal leaves very little room for the busbar and the interconnects.

4. Set float voltage and compensation at the controller. 2.23 V per cell at 25°C with −3 mV/°C/cell per °C per cell compensation applied by the charger, not by the battery. Hold float inside ±1% (±25 mV). Float current should stay below 5 mA per Ah — roughly 3.9 A for a 770Ah cell.

5. Confirm the charger current against the cell’s 160 A limit. Maximum charging current is 160 A, about 0.21C. A charger sized on the nominal bus voltage alone will routinely deliver more than that during a cold-morning recovery, and chronic overcharge is the most common cause of early float failure.

6. Demand the documentation and the destination approvals. IEC 60896-11:2002 and DIN 40736-1:1985 test reports, UL 1989, BS 6290 Part 4, Eurobat Long Life, GB/T 19638.2-2014 and YD/T 1360, plus the MSDS, UN2794 transport appraisal and certificate of origin. Where the destination requires SONCAP, PVOC, SASO, BIS or ESMA, establish who arranges it and the lead time before you commit.

7. Build the commissioning protocol into the scope. Initial electrolyte top-up, first full charge, a capacity test if the cells were stored, cell-to-cell voltage balance within ±0.05 V, and a photographed baseline per cell. Without that baseline, month-24 diagnosis is guesswork.

§5 — The Trust Layer: The Numbers You Should Memorise

Manufacturing controls you can verify before you energise the bank. CHISEN has manufactured stationary lead-acid since 2002, with 8 production bases and 70 GWh annual capacity. The OPzS line runs statistical process control on the four process steps that actually determine life: paste coating, plate-group assembly, formation and sealing. Every cell receives 100% outgoing inspection covering capacity, internal resistance, open-circuit voltage and visual condition. Third-party pre-shipment inspection by SGS, TUV, BV or CTI is available on request. Company details: about CHISEN Battery →.

End voltage by discharge rate (per IEC 60896 and GB/T 19638) — this is the table that decides whether a 770Ah cell is correctly specified.

Float voltage compensation reference.

Equalise at 2.35–2.40 V per cell monthly, with a −5 mV/°C compensation, and cap the duration at 24 hours.

The seven failure modes that shorten OPzS life, and what prevents each.

Commissioning checklist — do these before the first load test.

1. Check the electrolyte level and specific gravity on every cell; top with deionised or distilled water to the marked line. SG should read 1.240 ± 0.01 g/cm³ at 25°C.
2. Terminal torque check at 10–12 N·m. Photograph the torque wrench reading per string — that photograph is the document that surfaces in warranty disputes.
3. Cell-to-cell voltage spread within ±0.05 V before the string is commissioned. Anything wider requires an equalisation cycle before energising.
4. Confirm the charger float setpoint at 2.23 V per cell and temperature compensation at −3 mV/°C/cell at the controller, not just at the battery.
5. Log the baseline: per-cell voltage, specific gravity, ambient temperature and room position. Without that baseline you cannot diagnose anything at month 24.

Altitude derating (per GB/T 19638). Up to 3,000 m normal operation; above 3,000 m, derate approximately 8% of capacity for every additional 1,000 m; above 5,000 m requires a special low-pressure, reinforced-case variant. Railway, mining and high-altitude installations should carry that in the calculation, not discover it on site.

Safety. A 770Ah flooded cell produces approximately 3,900 A on direct short. Never place a metal tool across terminals. Charging generates hydrogen — no flames, no sparks, no smoking in the battery room. Wear eye protection and acid-resistant gloves; dilute sulphuric acid requires immediate 15-minute flush with clean water if it reaches the eye. Handle and dispose of cells under the UN2794 dangerous-goods procedure and never drain electrolyte into a floor drain.

§6 — FAQ: 9 Questions Stationary Procurement Teams Ask

Q1. What is the difference between OPzS2-770 and OPzV2-770? OPzS2-770 is flooded: liquid sulphuric acid in a transparent vented case, requiring a 3–6 month watering interval and upright installation only. OPzV2-770 is valve-regulated gel: sealed, maintenance-free, installable in any orientation except inverted. Both use tubular positive plates. Choose OPzS for staffed rooms and daily deep cycling; choose OPzV for unmanned or space-constrained sites.

Q2. How much usable capacity does a 770Ah cell actually deliver? 770Ah is the ten-hour rate rating to 1.80 V per cell. At the five-hour rate the same cell delivers roughly 700Ah, at the three-hour rate roughly 660Ah, and at one hour roughly 570Ah. Size your bank at the discharge rate your application actually runs at, not at the nameplate.

Q3. How many cells do I need for a 48V system? 24 cells in series for 48V, 30 for 60V, 54 for 108V (110V DC panel), 108 for 216V (220V industrial), and 190 for 380V three-phase DC. Always confirm the cell count against your actual DC panel nominal before ordering.

Q4. What float voltage should I set? 2.23 V per cell at 25°C, with temperature compensation of −3 mV/°C/cell per cell applied by the charger. Equalise monthly at 2.35–2.40 V per cell for no more than 24 hours, with an independent −5 mV/°C per cell compensation. Hold float inside ±1%.

Q5. How often does an OPzS2-770 need water? Every 3–6 months in a temperate room, more often in hot or dry climates. Check specific gravity monthly and top with deionised or distilled water to the marked line at 1.240 ± 0.01 g/cm³ at 25°C. Never top with tap water and never add acid.

Q6. What is the cycle life, and does it matter for my application? 1,500–2,500 cycles at 80% depth of discharge, 2,500–4,000 at 50% DOD, and 4,500–6,500 at 30% DOD. For pure float telecom duty the cycle figure is largely irrelevant and the 20–25 year float life at 25°C is what matters. It becomes the deciding number wherever the bank is cycled regularly — solar with evening peaks, rail signalling with track battery duties, or diesel engine starting packages.

Q7. Can I install it on its side? No. The flooded cell must be installed upright to prevent electrolyte leakage out of the vent plug. If your cabinet cannot accommodate upright cells, specify the sealed OPzV variant instead.

Q8. What documents ship with the battery? The standard export pack includes the commercial invoice, packing list, certificate of origin, MSDS, UN2794 transport appraisal and full IEC 60896 test reports. Product certification covers IEC 60896-11, DIN 40736-1, GB/T 19638.2, YD/T 1360, Eurobat Long Life, BS 6290 Part 4 and UL 1989. Destination approvals such as SONCAP, PVOC, SASO, BIS and ESMA are arranged on request.

Q9. What do I need to send for a quotation? Send the bus voltage and the cell count, the backup load and duration, the worst-case ambient temperature, the site situation (staffed room, container, or unattended), the altitude, and the destination country for documentation. We return a complete Excel sizing table with the quotation within 24 hours, and sample cells ship on request.

Expert Summary

For stationary procurement teams evaluating the OPzS2-770 2V770Ah, the decisive facts are these. It is a 2-volt stationary cell rated at 770 amp-hours at the ten-hour rate to 1.80 V per cell, built on a tubular positive plate with flooded dilute sulphuric-acid electrolyte at specific gravity 1.24 in a transparent vented SAN container, compliant with DIN 40736-1:1985 and IEC 60896-11:2002, with published dimensions of 254 × 210 × 471 mm and a total height of 525 mm, a Φ20-M8 terminal, a maximum charging current of 160 A, a maximum discharge current of 2,200 A over five seconds, an internal resistance of 0.55 mΩ fully charged at 25°C and a short-circuit current of 3,900 A. Tubular plate construction delivers 1,500–2,500 cycles at 80% depth of discharge, 2,500–4,000 at 50% and 4,500–6,500 at 30%, together with a 20+ year float design life at 20 °C that halves for every 10°C rise in ambient temperature. Float is 2.23 V per cell with −3 mV/°C/cell compensation and equalise 2.35–2.40 V per cell with −5 mV/°C. A single cell builds 24V, 48V, 60V, 108V, 216V and 380V strings at 12, 24, 30, 54, 108 and 190 cells respectively, with the same 770Ah string capacity in each case. Sizing errors overwhelmingly trace to using the C10 nameplate for a deeper duty, where real deliverable capacity falls to roughly 86% of specification at C3. In a modelled 48V telecom DC plant at 30°C ambient over a ten-year horizon, total cost of ownership per string is approximately $11,150 for flooded tubular, $9,500 for sealed tubular gel and $8,090 for LFP, with the flooded-versus-gel difference driven almost entirely by watering labour and one mid-life replacement rather than by purchase price. Two fields on the currently published model page — the discharge-rate table and the weight — are inconsistent with a 770Ah cell and should be confirmed against the current datasheet before an order is released. CHISEN supplies these cells factory-direct from 8 production bases with 70 GWh annual capacity, full CE / ISO 9001 / ISO 14001 / UL / IEC certification, export documentation prepared for more than 60 destination markets, third-party pre-shipment inspection on request, and free engineering sizing returned within 24 hours.

Contact CHISEN — 24-Hour Response

CHISEN Battery — 20+ years manufacturing stationary lead-acid, exporting to 60+ countries.

• Email: sales@chisen.cn — full quotation and sizing table within 24 hours
• Phone / WhatsApp: +86 131 6622 6999
• WhatsApp: https://wa.me/8613166226999
• Model page: https://www.chisen.cn/en/OPzS2-770/2V770Ah.html

Send us bus voltage and cell count + backup load and duration + worst-case ambient temperature + site situation + altitude + destination country, and our engineering team returns a complete sizing sheet — cell count, standard capacity selection, rack dimensions, temperature derating applied, charger profile and documentation scope — within one working day. Sample cells are available on request for your own capacity test before you commit to a full bank.

Related reading: for the sealed tubular alternative at the same capacity, see the OPzV series tubular gel battery specifications →. For cycle-life and TCO comparison across tubular and flat-plate technologies, see the tubular plate battery technical overview →. For the electric vehicle range that covers traction duties, see the EVF electric road vehicle series →. Full CHISEN product range across 2V, 6V, 8V and 12V voltages: lead-acid and lithium battery product catalogue →.

Published by CHISEN Battery. Standard data per CHISEN OPzS2-770 published datasheet, IEC 60896-11:2002 and DIN 40736-1:1985. TCO figures are a stated-assumption model for comparison, not a quotation. Two published fields on the source model page (discharge-rate table and weight) are pending verification and are not reproduced here as fact — request the current datasheet. Availability, certification and destination-specific approvals confirmed on request.