The output voltage of a charger should be

Question

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higher than the battery voltage

Explanation: To charge a secondary battery, the charger must provide an output voltage that is higher than the open-circuit voltage of the battery. This potential difference is necessary to overcome the internal resistance and the back EMF of the battery, allowing current to flow into the battery to reverse the chemical discharge reaction.

Working Principle: During charging, the battery acts as a load. According to Kirchhoff's Voltage Law, for current to flow from the charger into the battery, the charger's terminal voltage $V_{ch}$ must satisfy $V_{ch} = E_b + I(R_{int} + R_{line})$, where $E_b$ is the battery EMF, $I$ is the charging current, and $R_{int}$ is the internal resistance. If $V_{ch} \leq E_b$, no current (or a negligible amount) will flow into the cell.

Key Formulas: $V_{ch} = E_b + I \cdot R_{total}$ — Charging voltage requirement; $P_{in} = V_{ch} \cdot I$ — Input power for charging

Key Points: Charging is a process of converting electrical energy back into chemical energy.; A potential difference is mandatory to facilitate the flow of charging current.; Constant current (CC) and Constant voltage (CV) are common charging profiles.; If $V_{ch}

Advantages: Ensures effective storage of energy; Allows for controlled charging rates

Disadvantages: High potential difference can cause overheating if not regulated; Requires proper thermal management

Applications: Electric Vehicle (EV) fast charging; Smartphone and Laptop battery charging; Industrial UPS systems

Additional Info: The charging voltage is typically maintained slightly above the battery's nominal voltage to prevent damage while ensuring full charge.. Option A is incorrect because current would flow out of the battery, leading to discharge.. Option C is incorrect because no potential gradient exists, resulting in zero net current flow.

Answer: B is correct — The charger output voltage must exceed the battery voltage to overcome internal resistance and drive current into the cell.

Exam Tip: Remember the analogy of water flow: water flows from a higher pressure (potential) to a lower pressure; similarly, charge flows from a higher potential (charger) to a lower potential (battery).

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