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Examoogle • User • info@examoogle.com • EE-2024-8821
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The watt-hour efficiency of a lead-acid cell varies between
25 to 35%
40 to 60%
70 to 80%
90 to 95%
70 to 80%
Quick Summary: The watt-hour efficiency (energy efficiency) of a lead-acid cell typically ranges between 70% and 80%. This value represents the ratio of the output energy discharged from the battery to the input energy supplied during the charging process.
The watt-hour efficiency (energy efficiency) of a lead-acid cell typically ranges between 70% and 80%. This value represents the ratio of the output energy discharged from the battery to the input energy supplied during the charging process.
ηwh=WhinputWhoutput×100
Wh=∫0tV(t)⋅I(t)dt
The efficiency is limited by internal energy losses, primarily due to internal resistance (I2R losses) during charge/discharge cycles and electrochemical overpotential requirements. Furthermore, chemical side reactions, such as the electrolysis of water (gassing) during the final stages of charging, consume electrical energy that is not recovered during discharge, leading to energy dissipation as heat.
Watt-hour efficiency accounts for both current (Ampere-hour) efficiency and voltage variations.
Ampere-hour (Ah) efficiency is higher than watt-hour (Wh) efficiency, typically 85-95%.
Voltage during discharge is always lower than voltage during charge due to IR drop and polarization.
Efficiency is affected by the rate of charge/discharge and the operating temperature.
High reliability for stationary applications.
Good performance in high-rate discharge conditions.
Energy loss due to internal resistance.
Requires careful maintenance to prevent plate sulfation.
Automotive starter batteries.
Uninterruptible Power Supply (UPS) systems.
Standby power for telecommunication stations.
Ah efficiency is defined as AhinAhout. Since discharge voltage is lower than charging voltage, ηwh is strictly less than ηAh.
Option A (25-35%) is too low; Option B (40-60%) underestimates battery performance; Option D (90-95%) is technically impossible due to thermodynamic losses.
C is correct — The watt-hour efficiency of a lead-acid cell is typically in the range of 70% to 80%.
Remember that energy efficiency (etaWh) is always lower than charge efficiency (etaAh) because the discharge voltage is inherently lower than the charging voltage.