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The lead-acid cell should never be discharged beyond
1.8 V
1.9 V
2 V
2.1 V
1.8 V
Quick Summary: A lead-acid cell should not be discharged below 1.8 V because doing so promotes the formation of large, hard lead sulfate crystals on the plates, a process known as sulfation. This chemical change is difficult to reverse and permanently reduces the battery's capacity and overall service life.
A lead-acid cell should not be discharged below 1.8 V because doing so promotes the formation of large, hard lead sulfate crystals on the plates, a process known as sulfation. This chemical change is difficult to reverse and permanently reduces the battery's capacity and overall service life.
VcellтАЛ=EтИТIтЛЕr тАФ Terminal voltage calculation during load discharge
PbO2тАЛ+Pb+2H2тАЛSO4тАЛтЖТ2PbSO4тАЛ+2H2тАЛO тАФ Chemical reaction at discharge
During discharge, active material on both the positive (lead dioxide, PbO2тАЛ) and negative (spongy lead, Pb) plates converts into lead sulfate (PbSO4тАЛ). If discharge continues below 1.8 V, the electrolyte density drops significantly, and the PbSO4тАЛ converts into a stable, crystalline form that occupies more volume. This accumulation causes plate warping, internal short circuits, and loss of electrolyte porosity, effectively 'killing' the cell.
Nominal voltage of a lead-acid cell is 2.0 V.
Sulfation occurs when a battery is left in a discharged state for too long.
Specific gravity of the electrolyte is a reliable indicator of state-of-charge.
Deep discharge cycles significantly shorten cycle life.
High surge current capability
Low internal resistance
Cost-effective for high capacity applications
Heavy weight due to lead plates
Sensitive to deep discharge cycles
Electrolyte leakage risk
Automotive starter batteries
Uninterruptible Power Supplies (UPS)
Emergency lighting systems
The 1.8 V limit is the 'cut-off' voltage for a standard 2 V cell.
Option B (1.9 V) is near full discharge but safe; 1.8 V is the absolute safety threshold.
Option C (2 V) is the nominal voltage, not a discharge limit.
A is correct тАФ The 1.8 V threshold is established to prevent irreversible chemical damage through sulfation.
Always remember that lead-acid batteries fail prematurely due to deep discharge; keep them charged to maintain an electrolyte density of roughly 1.250-1.280 for optimal performance.