OPzS2-500 2V500Ah Tubular Flooded Battery — Telecom, DC Panel and Solar Buyer’s Guide (2026)

Reading time: 21 minutes | For: telecom power engineers, utility DC panel specifiers, solar EPC contractors, railway signalling engineers, industrial distributors and OEM buyers

Answer First

The OPzS2-500 2V500Ah is a 2-volt, 500 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 a site has a staffed room, a maintenance budget, and a duty cycle that rewards deep cycling rather than pure float standby.

Five numbers decide the procurement:

• 500Ah at C10 (10-hour rate to 1.80 V/cell) places it in the most-quoted capacity band for 48V, 110V and 220V DC backup — between the 420Ah and 600Ah steps, which is where most utility and telecom specifications land.
• One cell, four bus voltages: 24 cells = 48V, 54 cells = 108V (110V DC panel), 108 cells = 216V (220V industrial), 190 cells = 380V three-phase DC.
• 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.
• 3,700 A short-circuit current and 0.50 mΩ internal resistance, giving better voltage retention under the high-rate pulses that data-centre and railway UPS strings actually produce.
• Transparent SAN container — you can see the electrolyte level and plate condition from the aisle. No IR camera, no guesswork.

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 we will quantify it below.

Key Takeaways

1. OPzS2-500 2V500Ah = 2V nominal cell, 500Ah at C10, tubular positive plate, flooded electrolyte, vented transparent case. Built to DIN 40736-1 / IEC 60896-11.
2. Tubular flooded outperforms tubular gel on cycle life, and flat-plate AGM on everything else. 1,500–2,500 cycles at 80% DOD versus roughly 500–1,000 for flat-plate AGM.
3. Maintenance is the real trade-off, not purchase price. OPzS costs less up front than OPzV, but demands a 3–6 month watering route. Over a 20-year life the total cost of ownership favours OPzS in staffed rooms and OPzV in unmanned ones.
4. Capacity derates hard above 35°C. Float life halves for every 10°C rise (Arrhenius): 25°C ≈ 20 years, 35°C ≈ 10 years, 45°C ≈ 5 years. Site thermal design is a battery-life decision.
5. Sizing is almost always done on the wrong discharge rate. A 500Ah cell delivers ~420Ah at the 3-hour rate and ~357Ah at the 5-hour rate. 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.

§1 — What Is the OPzS2-500 2V500Ah, Precisely?

The CHISEN OPzS2-500 is a single 2-volt stationary cell, not a 12V monobloc. It is one element in a series string, and the string voltage is set purely by how many elements you wire together.

Model decoding under DIN 40736-1:

Why the tubular plate is the core of the product. A conventional flat-plate positive uses a cast grid whose ribs corrode progressively as the cell cycles, and whose active material sheds as it expands and contracts. The OPz plate casts the positive active material into glass-fibre tubes around a central current collector rod. Active material is retained mechanically by geometry rather than by grid integrity. This is the single reason tubular cells tolerate deep discharge and high-temperature float service without the plate collapse that ends flat-plate life.

Flooded versus gel — the chemistry that matters. Both are tubular. They differ in how the electrolyte behaves:

• OPzS (flooded, DIN 40736-1): liquid sulphuric acid at 1.240 g/cm³ specific gravity, open container with a flame-arrestor vent plug, acid-absorbing anti-corrosion plug. Water evaporates and must be replaced.
• OPzV (valve-regulated gel, DIN 40472): silica-gelled electrolyte immobilised in a colloidal matrix, sealed case with a one-way relief valve. Nothing to top up.
• AGM (flat plate): electrolyte suspended in a glass-fibre mat, sealed, flat plates. Cheapest, shortest life.

The flooded cell’s advantage is direct access to the chemistry. Because the electrolyte is liquid, an engineer can measure specific gravity, check level, and correct for stratification on site. That is diagnostically powerful and it is not available in a sealed cell. The disadvantage is that every one of those maintenance actions is labour.

§2 — Quick Specifications — OPzS2-500 2V500Ah

§3 — Standards, Certifications and the Compliance Gate

For a 2V flooded stationary cell the compliance question is narrower than for lithium, but it is not optional. In most export markets a battery that lacks the correct declaration does not clear customs, regardless of how good the cell is.

Destination-country gates you should plan for before the PO, not after. These are not product standards — they are import clearances, and they are the most common cause of a delayed shipment:

• SONCAP (Nigeria), PVOC (Kenya), SASO (Saudi Arabia), BIS (India), ESMA (UAE) — pre-shipment conformity verification requiring a third-party inspection certificate.
• CE marking for EU-bound consignments under the applicable battery directives.
• RoHS / REACH / WEEE declarations for European distribution.

CHISEN prepares the standard export pack — commercial invoice, packing list, certificate of origin, MSDS, UN2794 transport appraisal, and full IEC 60896 test reports — and coordinates SGS / TUV / BV / CTI inspection on request. If you need a destination-specific certification handled, raise it at RFQ stage; it is materially faster than adding it after the container is booked.

§4 — The Pain: Why 500Ah Flooded Procurement Goes Wrong

The pain is rarely the cell. It is the four decisions that happen before anyone checks the cell.

1. The C-rate mismatch. The catalogue says 500Ah. Your discharge profile is not a 10-hour profile. A 500Ah cell delivers approximately 420Ah at the 3-hour rate and 357Ah at the 5-hour rate. If you size on the nameplate number and your site actually runs a 3-hour discharge, your real usable capacity is 84% of what you specified — and that error compounds across 108 series cells. This is the single most common cause of undersized backup cabinets in the field.

2. The “nobody came in 14 months” failure. A flooded cell left unmaintained in a 40°C room loses water through the vent plug, the electrolyte level drops below the plate bridge, and the cell sulfates irreversibly. The failure is not dramatic and it is not attributable — it surfaces as a bank that will not hold charge eighteen months after commissioning, at which point the whole string is normally replaced.

3. The OPzV-vs-OPzS mismatch. Buyers frequently specify the sealed tubular gel because “gel is better”, then deploy it in a railway signalling hut in Gujarat where ambient hits 48°C for six months of the year. Gel is superior on cycle life at moderate temperature and inferior on sustained high-temperature float, because the sealed case has no mechanism to shed the heat generated by oxygen recombination. In that environment the flooded OPzS outlasts the gel by a wide margin.

4. Container geometry specified too late. The OPzS2-500 is 166 mm wide and 525 mm tall including terminals. A standard 19-inch rack shelf with 100 mm of airflow clearance will not take a 108-cell string of these in the orientation most drawings assume. Racks are ordered on the DC panel schedule, which is frequently produced before the battery make is fixed. Verify the rack against the actual cell drawing, not the nominal footprint.

§5 — The Choice: OPzS2-500 vs OPzV2-500 vs AGM 2V 500Ah

This is the comparison that decides your project. All three are available at 2V 500Ah; they are not interchangeable.

The decision rule, stated plainly:

A note on how these numbers are read. Cycle-life figures quoted as a single number are meaningless without the depth of discharge and the temperature. “2,000 cycles” at 50% DOD is a better battery than “1,500 cycles” at 80% DOD. Always ask for the cycle count at your actual DoD, and at 25°C, before comparing any two datasheets.

§6 — Capacity Sizing: Getting the Number Right

The standard engineering relationship for a backup bank:

Battery capacity (Ah) = Load power (W) × Backup duration (h) ÷ Bus voltage (V) ÷ Inverter efficiency ÷ Temperature factor

Where inverter efficiency is 0.85 for UPS and 1.0 for a pure DC load, and the temperature factor is 1.0 at 25°C, 0.85 at 35°C and 0.70 at 45°C. Always reserve a 20–30% margin above the calculated figure.

Worked example 1 — telecom base station, 48V. Load 1.5 kW, 4-hour backup before generator start, 48V bus, UPS efficiency 0.85, 25°C.

Capacity = 1500 × 4 ÷ 48 ÷ 0.85 × 1.0 ≈ 147 Ah → select 150Ah cells (24 in series for 48V) with ~20% margin. Above 35°C, add the derating factor: 147 ÷ 0.85 ≈ 173 Ah, which pushes the selection to the 200Ah step.

Worked example 2 — solar with backup, 48V. 5 kW hybrid inverter, 4 hours of autonomy, 48V bus, 0.85 efficiency, 25°C.

Capacity = 5000 × 4 ÷ 48 ÷ 0.85 × 1.0 ≈ 490 Ah → OPzS2-500 at 24 cells in series. This is precisely the configuration where the flooded tubular cell earns its place: daily cycling at meaningful depth is where its 1,500–2,500 cycle rating pays back against the flat-plate alternative.

Worked example 3 — 110V substation DC panel. 0.8 kW control and protection load, 10-hour backup, 110V bus, DC load efficiency 1.0, 25°C.

Capacity = 800 × 10 ÷ 110 ÷ 1.0 × 1.0 ≈ 73 Ah → 54 cells in series to 108V, selecting the 100Ah step with margin.

Worked example 4 — 220V three-phase industrial DC. 150 kW, 30-minute full-load backup, 220V bus, 1.0 efficiency.

Capacity = 150000 × 0.5 ÷ 220 ≈ 341 Ah → 108 cells in series to 216V, selecting the 420Ah step for margin.

Series-string arithmetic you will need repeatedly:

The five-step selection procedure:

1. Confirm bus voltage and cell count. Telecom, solar, UPS, railway, medical and marine applications all run on one of the four configurations above.
2. Calculate required capacity using the formula, then apply the temperature factor for your worst-case ambient.
3. Select the nearest standard capacity — 100 / 200 / 300 / 500 / 1,000 / 1,500 / 2,000 / 3,000 Ah — keeping a 20–30% margin.
4. Confirm the physical fit. 166 mm wide, 470 mm body height, 525 mm total height, 26.0 kg. Allow ≥50 mm rear clearance for airflow and check the rack against the drawing.
5. Confirm standards, certification and service. Tender documents, customs clearance and destination-country certification should be settled at RFQ stage.

Discharge performance reference for the OPzS2-500 class (10-hour rate to 1.80 V/cell, 25°C):

If you are unsure about any of this: send us the system voltage, load power, backup duration and worst-case ambient temperature, and CHISEN returns a complete sizing table in Excel with a quote inside 24 hours. That is a free engineering service, not a sales tactic — the sizing is the part where mistakes are most expensive.

§7 — Float Voltage, Temperature Compensation and the Temperature Derating Trap

Float voltage: 2.24 V/cell at 25°C, compensated at −3.3 mV per °C per cell.

V_float (actual) = 2.24 V + (−3.3 mV/°C) × (measured temperature − 25°C)

Hold float voltage inside ±1% (±25 mV). Outside that band, life shortens measurably. Float current should stay below 5 mA per Ah — roughly 2.5 A for a 500Ah cell. Equalise at 2.35–2.40 V/cell monthly, with a −5 mV/°C compensation, and cap the duration at 24 hours.

The temperature derating trap. This is the number most often missed in hot-climate projects. Float life follows the Arrhenius rule: every 10°C rise roughly halves float life.

A 20-year cell installed in a 45°C unventilated container room delivers roughly five years. No cell chemistry fixes this; only thermal design does. Specify the cell for the worst ambient, and design the room to keep the average below 30°C.

Altitude derating (per GB/T 19638): up to 3,000 m normal operation; above 3,000 m, derate approximately 8% capacity for every additional 1,000 m; above 5,000 m requires a special low-pressure, reinforced-case variant. Railway and Andes installations should be sized with this in the calculation, not discovered on site.

§8 — The Trust Layer: What Actually Determines 20-Year Delivery

Manufacturing controls you can verify before you wire the balance.

CHISEN has manufactured stationary lead-acid since 2002, with 8 production bases and 70 GWh annual capacity. The OPzS line runs SPC 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.

Supply and service footprint. More than 60 destination countries, with technical support in English, Chinese, Spanish, French, Arabic, Russian and Vietnamese. Twelve-hour email response, 24-hour complete quotation, 48-hour engineered solution for complex projects.

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

Commissioning checklist — do these before the first load test.

1. Check 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 — this is the number 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 charger float setpoint at 2.24 V/cell and temperature compensation at −3.3 mV/°C/cell at the controller, not just at the battery.
5. Log the baseline: per-cell voltage, SG, ambient temperature and room position. Without this baseline you cannot diagnose anything at month 18.

End-voltage reference by discharge rate (per IEC 60896 / GB/T 19638):

Safety. A 500Ah flooded cell produces approximately 3,700 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; never drain electrolyte into a floor drain.

§9 — FAQ: 12 Questions Procurement Teams Actually Ask

Q1. What is the difference between OPzS2-500 and OPzV2-500?

OPzS2-500 is flooded: liquid sulphuric acid in a transparent vented case, requiring a 3–6 month watering interval, installed upright only. OPzV2-500 is valve-regulated gel: sealed, maintenance-free, installable in any orientation except inverted. Both use tubular positive plates and both carry a 20+ year float design life at 25°C. Choose OPzS for staffed rooms and daily deep cycling; choose OPzV for unmanned or space-constrained sites.

Q2. How much usable capacity does a 500Ah cell actually deliver?

500Ah is the 10-hour rate rating. At the 3-hour rate the same cell delivers roughly 420Ah, at the 5-hour rate roughly 357Ah, and at 1 hour roughly 265Ah. 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, 54 cells for 108V (110V DC panel), 108 cells for 216V (220V industrial), and 190 cells 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?

2.24 V/cell at 25°C, with temperature compensation of −3.3 mV/°C/cell applied by the charger. Equalise monthly at 2.35–2.40 V/cell for no more than 24 hours, with an independent −5 mV/°C/cell compensation.

Q5. How often does an OPzS2-500 need water?

Every 3–6 months in a temperate room, more frequently 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 or add acid.

Q6. What is the cycle life of the OPzS2-500?

1,500–2,500 cycles at 80% depth of discharge, and 2,500–4,000 cycles at 50% DOD, at 25°C. Flat design life is 20–25 years at 25°C float. Both figures halve for every 10°C rise in ambient temperature.

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 is the internal resistance and short-circuit current?

Internal resistance is approximately 0.50 mΩ fully charged at 25°C, and short-circuit current is approximately 3,700 A per the datasheet. Max recommended discharge current is 1,500 A over 5 seconds, and maximum charging current is 100 A (0.20 C10).

Q9. How long can it be stored without charging?

At 25°C, self-discharge is 3% per month, giving a 9–12 month shelf life without a recharge. Store fully charged in a dry, ventilated environment between −25°C and +45°C, away from direct sunlight and corrosive gases, and top up every 3–6 months. Cells stored beyond 12 months should be capacity-tested before returning to service.

Q10. What certifications and documents ship with the battery?

The standard export pack includes 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-country approvals such as SONCAP, PVOC, SASO, BIS and ESMA are arranged on request.

Q11. What are the physical dimensions and weight?

166 × 206 × 470 mm with a total height of 525 mm including the Φ20-M8 terminals, at 26.0 kg including electrolyte. Terminal torque is 10–12 N·m. Allow at least 50 mm clearance behind the string for airflow and verify your rack against the cell drawing before ordering.

Q12. How do I get a quote and sizing?

Send system voltage, load power, backup duration and worst-case ambient temperature to sales@chisen.cn, or message +86 131 6622 6999 on WhatsApp at https://wa.me/8613166226999. CHISEN returns a complete Excel sizing table with quotation within 24 hours. Sample cells ship on request.

Expert Summary

For industrial buyers evaluating the OPzS2-500 2V500Ah, the decisive facts are these. It is a 2-volt stationary cell rated at 500 amp-hours at the ten-hour rate, built on a tubular positive plate with flooded liquid electrolyte in a transparent vented case, compliant with DIN 40736-1 and IEC 60896-11. Its 166 × 206 × 470 mm footprint and 26 kg cell weight stack into 48V, 110V, 220V and 380V strings at 24, 54, 108 and 190 cells respectively. Tubular plate construction delivers 1,500–2,500 cycles at 80% depth of discharge — approximately 1.5 to 2 times the cycle life of a flat-plate AGM at the same amp-hour rating — together with 0.50 mΩ internal resistance and 3,700 A short-circuit current. Float voltage is 2.24 V per cell at 25°C with −3.3 mV/°C/cell temperature compensation, and float design life is 20 to 25 years at 25°C, halving for each additional 10°C of ambient temperature. The cell requires a 3–6 month watering interval, upright installation only, and an on-site maintenance route; where none of those exist, the sealed tubular gel OPzV2-500 is the lower total-cost choice despite a 15–25% higher purchase price. Sizing errors overwhelmingly trace to using the C10 nameplate rating for a C3 duty cycle, where real deliverable capacity falls to roughly 84% of specification. 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, 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
• Website: https://www.chisen.cn

Send us system voltage + load power + backup duration + worst-case ambient temperature, and our engineering team returns a complete sizing sheet — cell count, standard capacity selection, rack dimensions, temperature derating applied — 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 →. 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 OPzV/

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