Difficulty: Easy
Correct Answer: applying a DC voltage of correct polarity slightly higher than the battery EMF
Explanation:
Introduction / Context:
Understanding how to properly charge a lead–acid battery is essential for safety, service life, and electrical system reliability. This question focuses on the correct principle of recharging rather than common but incorrect workshop myths like ‘‘just add acid’’ to fix a low battery.
Given Data / Assumptions:
Concept / Approach:
Charging requires an external DC source of the correct polarity and a voltage slightly above the battery’s open-circuit EMF so that current flows into the battery. Modern chargers and alternators regulate voltage and current to avoid overcharge. Adding acid does not charge a battery; it only changes specific gravity and can damage plates. Reversing polarity risks severe damage and safety hazards.
Step-by-Step Solution:
Identify the goal: restore charge by forcing current into the battery.Ensure correct polarity: positive to positive, negative to negative.Apply a controlled voltage slightly higher than EMF (e.g., ~14.0–14.4 V for a 12 V battery in cyclic charge).Avoid chemical shortcuts like adding acid; only top up with distilled water to cover plates.
Verification / Alternative check:
Vehicle alternators regulate around 13.8–14.4 V while the engine runs, demonstrating the principle of charging with a voltage above the battery EMF.
Why Other Options Are Wrong:
Adding distilled water merely corrects level; no charging occurs. Adding sulphuric acid alters chemistry, accelerates corrosion, and is unsafe. Reversing polarity causes damage and is never used to charge a healthy battery.
Common Pitfalls:
Confusing specific gravity correction with state-of-charge recovery; using unregulated chargers that overheat batteries; ignoring temperature compensation.
Final Answer:
applying a DC voltage of correct polarity slightly higher than the battery EMF
Discussion & Comments