What is a lead acid battery
A lead acid battery is a rechargeable electrochemical cell using lead metal and lead dioxide electrodes immersed in dilute sulphuric acid electrolyte. Invented by Gaston Planté in 1859, it is the oldest commercial rechargeable battery and remains in widespread use for automotive starting, uninterruptible power supplies, telecom backup and cost-sensitive solar off-grid systems.
For Indian solar, lead acid is the legacy chemistry that powered the rural off-grid revolution from 2000 to 2020. Tubular flooded lead acid was the workhorse for solar home systems, telecom towers and small commercial backup. From 2022 onward, LFP has displaced lead acid in most new installations, but lead acid remains relevant in cost-sensitive segments and in automotive applications.
Major Indian manufacturers include Exide, Amara Raja, HBL Power Systems, Su-kam, Luminous and Tata Green Batteries (see our Exide vs Amaron battery comparison for a head-to-head). India’s lead acid recycling industry is one of the most mature globally, recovering over 95 percent of lead content.
Lead acid battery explained simply
A lead acid battery has lead plates in a sulphuric acid bath. When you charge it, the acid concentration rises and the plates store energy. When you use it, the plates react with the acid to release current. It is heavy, low-energy-density and needs occasional water top-up, but it is cheap and well understood.
Why lead acid still matters
Cost. Lowest upfront cost per kWh of any commercial chemistry (see our solar battery price guide for current ranges).
Indian manufacturing maturity. Decades of domestic supply chain, recycling and service network.
Recycling. Over 95 percent of lead content is recovered and reused.
Niche fit. UPS standby, automotive starting, cost-sensitive small solar.
Lower thermal runaway risk than NMC lithium.
How lead acid works
Discharging:
- At the negative electrode (lead sponge), Pb + SO4²⁻ → PbSO4 + 2e⁻
- At the positive electrode (lead dioxide), PbO2 + 4H⁺ + SO4²⁻ + 2e⁻ → PbSO4 + 2H2O
- Lead sulphate forms at both electrodes.
- Acid concentration decreases.
Charging reverses the reactions, dissolving lead sulphate back into lead and lead dioxide.
Technical deep dive
Variants
| Type | Construction | Use case |
|---|---|---|
| Tubular flooded | Tubular positive plate, flat negative | Indian off-grid solar, UPS |
| Flat plate flooded | Flat plates both sides | Automotive starting |
| VRLA AGM | Absorbed glass mat separator, recombinant | Sealed UPS, telecom |
| VRLA gel | Gelled electrolyte | Premium sealed applications |
Cell voltage
Nominal: 2.0 V per cell. A 12 V battery has 6 cells. A 48 V bank has 24 cells.
| Charge stage | Per cell | 12 V battery |
|---|---|---|
| Float | 2.25 V typical | 13.5 V |
| Bulk | 2.4 V | 14.4 V |
| Equalisation | 2.5 to 2.6 V | 15 to 15.5 V |
Cycle life vs DoD
| DoD | Approximate cycles |
|---|---|
| 100% | 250 to 400 |
| 80% | 350 to 550 |
| 50% | 800 to 1,500 |
| 30% | 1,500 to 3,000 |
For solar service, 50 percent depth of discharge is the practical sweet spot for tubular flooded, and it directly sets the pack’s usable cycle life.
Specific gravity
| State | Specific gravity at 27°C |
|---|---|
| Full charge | 1.265 to 1.275 |
| 50% SOC | 1.225 |
| Discharged | 1.155 to 1.180 |
Hydrometer reading is the most reliable state of charge indicator for flooded lead acid.
Real-world applications
Rural off-grid solar. Tubular flooded packs of 200 to 1,000 Ah at 12 or 24 V, often paired with an off-grid inverter and installed as part of turnkey residential solar installations in unelectrified or low-reliability areas.
UPS systems. Indoor flat plate or VRLA AGM, designed for standby with occasional discharge (see our UPS glossary entry for how these systems differ from solar inverters).
Telecom backup. Historically VRLA AGM, increasingly being replaced by LFP.
Automotive starting. Flat plate flooded, designed for short high-current bursts.
Inverter home backup. Tubular flooded packs in residential power backup systems.
Solar streetlights (older). Sealed maintenance-free batteries, mostly replaced by LFP in new deployments.
Advantages
Lowest upfront cost.
Mature Indian manufacturing and recycling.
Robust under heavy current draws.
Tolerant to brief overcharging.
Well-understood failure modes.
Wide ambient operating range for short cycles.
Limitations
Short cycle life under deep cycling.
Heavy. Energy density 30 to 50 Wh/kg against 90 to 160 for LFP.
Maintenance required for flooded types.
Performance degrades sharply above 30 degrees Celsius.
Round-trip efficiency 75 to 85 percent against 92 to 95 for LFP.
Lead toxicity requires careful handling.
Common problems
Premature failure. Almost always traceable to chronic deep cycling below 50 percent SOC, missed top-up, or high temperature — see how long solar batteries actually last in Indian conditions for typical failure timelines.
Sulphation. Hardened lead sulphate on plates that does not dissolve. Battery shows full voltage but no capacity.
Acid stratification. Heavy acid sinks to the bottom. Equalisation mixes it back.
Plate shedding. Active material falls off, accumulates at the bottom, eventually shorts cells.
Negative grid corrosion. End-of-life failure mode for flooded.
Thermal runaway in VRLA at high temperature.
Best practices
Choose deep-cycle tubular for solar, not automotive starting batteries.
Set the charge controller to the right chemistry profile.
Monthly top-up with distilled water for flooded.
Quarterly equalisation cycle.
Maintain ambient temperature below 30 degrees Celsius.
Cycle within 50 percent DoD for best life.
Annual specific gravity check on each cell.
Replace as a bank, not individual cells.
Comparison: lead acid vs LFP vs NMC
Modern lithium-ion battery chemistries outperform lead acid on nearly every metric except upfront cost. For a full head-to-head on real-world Indian pricing and lifespan, see our lithium vs lead-acid battery comparison.
| Feature | Tubular lead acid | LFP | NMC |
|---|---|---|---|
| Cycles at 80% DoD | 350 to 550 | 4,500 to 6,000 | 2,000 to 4,000 |
| Energy density (Wh/kg) | 30 to 50 | 90 to 160 | 150 to 250 |
| Round-trip efficiency | 75 to 85% | 92 to 95% | 93 to 96% |
| Upfront cost (₹/kWh) | 8,000 to 15,000 | 40,000 to 70,000 | 50,000 to 90,000 |
| Lifecycle cost (₹/kWh-cycle) | 15 to 30 | 6 to 12 | 10 to 18 |
| Best fit | Rural off-grid, UPS standby | Daily-cycling solar | High-density EV |
Indian market context
Tubular flooded lead acid is still the default in rural and small home off-grid solar under MNRE solar lantern and home system programmes.
Telecom operators have shifted most new tower deployments to LFP. Existing lead acid banks are being phased out as they reach end of life.
Recycling is mandated under Battery Waste Management Rules 2022, with extended producer responsibility on manufacturers.
Major brands include Exide, Amara Raja, HBL, Su-kam, Luminous and Tata Green Batteries; our best solar battery brands in India roundup compares them across chemistries. Correctly sizing whichever bank you choose matters as much as the brand — SurgePV’s battery sizing guide walks through the calculation.
For PM Surya Ghar net-metered systems, batteries are not subsidised; both lead acid and LFP can be used for backup as user choice.
Standards and certifications
| Standard | Scope |
|---|---|
| IS 13369 | Stationary lead acid batteries with tubular positive plates |
| IS 1652 | Stationary cells and batteries |
| IS 1146 | Lead acid storage batteries general |
| IEC 60896 | Stationary lead acid batteries |
| IEEE 1188 | Maintenance for VRLA |
| Battery Waste Management Rules 2022 | Recycling and EPR |
Common mistakes
Using automotive starting batteries for solar cycling.
Chronic operation below 50 percent SOC.
Skipping water top-up for flooded.
Skipping monthly equalisation.
Mounting in unventilated hot enclosures.
Mixing old and new batteries in the same bank.
Setting charge controller to wrong chemistry profile.
Key takeaways
Lead acid is the legacy chemistry for cost-sensitive solar storage. Tubular flooded delivers 5 to 7 years of service at 50 percent DoD with proper maintenance. LFP has displaced lead acid in most new daily-cycling solar applications because of better lifecycle economics. Lead acid retains relevance in UPS standby, automotive starting and the lowest-cost rural off-grid segment.
Further reading
For how Lead Acid Battery plays out in real projects, these guides go deeper:
- Lithium vs Lead-Acid Solar Battery for Indian Homes
- Best Solar Battery Brands in India 2026
- How Long Do Solar Batteries Last in India?
- Solar Battery Price Guide India 2026
Sources
- IS 13369, IS 1652, IS 1146, Bureau of Indian Standards.
- IEC 60896, IEEE 1188, international lead acid standards.
- Battery Waste Management Rules 2022, Ministry of Environment, Forest and Climate Change.
- Exide, Amara Raja, HBL Power Systems product documentation.
- BloombergNEF Battery Price Survey 2024.
- Linden’s Handbook of Batteries (Reddy, T., editor), McGraw-Hill.
- Berndt D., Maintenance-Free Batteries, Wiley.
- IEA Energy Storage Outlook 2024.
- IRENA Battery Storage for Renewables.
Frequently Asked Questions
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Co-founder & CEO driving Qbits Energy's product strategy and growth across India.