Over charging of chemical battery

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Examoogle · Accepted Answer

all of the above

Explanation: Overcharging a lead-acid battery involves forcing current through it after it has reached full capacity, causing the electrolyte to decompose and the internal components to overheat. This leads to physical degradation of the battery structure and reduction of its chemical efficiency.

Working Principle: During overcharging, the energy is no longer stored chemically but causes electrolysis of water into $H_2$ and $O_2$ gases. The resulting rise in internal temperature causes the plates to expand and contract, leading to physical deformation (buckling), while the aggressive gas evolution physically dislodges the active lead-dioxide or lead-sponge material from the plate grids.

Key Formulas: $2H_2O + 	ext{energy} ightarrow 2H_2 \uparrow + O_2 \uparrow$ — electrolysis reaction causing gassing

Key Points: Electrolysis occurs when the charging voltage exceeds the gassing voltage of the electrolyte.; Excessive heat leads to irreversible damage to separators and plate structures.; Buckling of plates can lead to internal short circuits within the battery cell.; Active material loss significantly reduces the amp-hour capacity of the battery.

Advantages: Proper charging maintains optimal capacity; Correct terminal voltage prolongs cycle life

Disadvantages: High gassing pressure may rupture the casing; Permanent capacity loss due to material shedding

Applications: Lead-Acid Battery Maintenance; Power Electronics System Design

Additional Info: Overcharging is specifically damaging to VRLA batteries as it causes them to vent electrolyte, which cannot be replaced.. Option A, B, and C are all primary failure modes induced by prolonged overcharging.

Answer: D is correct — Overcharging initiates a cascade of chemical and physical failures including gassing, shedding of active material, and thermal expansion leading to structural buckling.

Exam Tip: Always remember that charging a battery is an endothermic-to-exothermic transition; keep charging voltage within the manufacturer's specified floating/cycling limits to prevent these failure modes.

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