Automotive electricals — main function of the battery In a conventional passenger car, what is the primary duty of the storage battery within the electrical system?

Introduction / Context:
The automotive battery and alternator form a complementary pair. Knowing their roles helps in diagnosing starting problems and charging faults.

Given Data / Assumptions:

• Vehicle uses a standard 12 V lead-acid battery (or equivalent chemistry) and an alternator with a regulator.
• Engine-driven alternator supplies power once the engine is running.
• Power demand during cranking is high for a short duration.

Concept / Approach:
The battery's primary function is to deliver high current to the starter motor to crank the engine from rest. It also buffers voltage, powers accessories with engine off or at idle, and bridges transient loads. However, when the engine is running above idle, the alternator normally supplies most electrical power and recharges the battery.

Step-by-Step Solution:
Identify starting requirement: starter motors may draw hundreds of amperes.Only the battery can supply this instantaneous current at engine standstill.Once running, alternator takes over load and charges battery.Therefore, the battery's main task is to power the starter during engine start.

Verification / Alternative check:
Service manuals specify cold-cranking amps (CCA) as the key battery rating, underscoring its primary role in starting.

Why Other Options Are Wrong:
The alternator supplies electricity to the vehicle when running, not the reverse.

The battery does stabilize voltage but that is secondary to starting duty.

Continuous powering during normal running is alternator's job.

Voltage regulation is handled by the alternator's regulator, not the battery.

Common Pitfalls:
Misattributing charging issues to the battery when the alternator or regulator is faulty; ignoring parasitic drains that deplete the battery between starts.

Final Answer:
Provide a large burst of power to crank the starter motor when starting the engine