ASE P2 TEST PRIMER: Battery, Charging and Starting Systems

ASE P2 TEST PRIMER: Battery, Charging and Starting Systems

The battery stores energy to provide starting and reserve power for the electrical system. Lead-acid batteries must be maintained at or near full charge for maximum life (average life is 4 to 5 years).



The major components include the battery (12-volt, lead-acid, wet-cell, Absorbent Glass Mat (AGM) or gel cell), battery cables (positive cable connection to electrical system and negative cable to ground), alternator (recharges the battery and provides current to power vehicle’s lights, electronics and electrical accessories), starter (conventional, gear reduction or permanent magnet) and starter solenoid or relay and ignition switch.

The battery stores energy to provide starting and reserve power for the electrical system. Lead-acid batteries must be maintained at or near full charge for maximum life (average life is 4 to 5 years). Battery problems can be caused by undercharging, dirty or loose battery cables, excessive heat or vibration. Replacement batteries must be the same or compatible Group Size (length, width, height and post configuration) and have the same or higher Cold Cranking Amp (CCA) rating as the original battery.
A battery’s state of charge can be measured with a voltmeter. A fully charged battery should read about 12.67 volts.

The condition of the battery can be tested with a carbon pile “load tester” that applies a calibrated load to the battery, or by using an electronic tester that measures the battery’s conductance (internal resistance). Accurate load testing requires a battery to be 75 percent or more charged (12.4 volts or higher). Battery charge doesn’t matter with conductance testing. If a battery won’t accept or hold a charge, or it tests “bad” by either testing method, it needs to be replaced.

Replacement batteries are dry-charged at the factory, but may require additional charging prior to installation. Battery and cable posts should be clean and tight to assure good electrical contact. Any missing or damaged engine ground cables also should be replaced.

The alternator is belt-driven and generates Alternating Current (AC), which is converted to Direct Current (DC) by diodes in the back of the unit. Many alternator failures are due to diode failures caused by overloading or overheating. An alternator should be bench tested to measure its voltage and current output. If output is less than specifications, the alternator needs to be replaced. If a questionable alternator tests good but the vehicle has a charging problem, the fault is not the alternator but something else such as wiring, voltage regulation control, battery cables, etc.).

The starter motor must crank at a certain RPM to start the engine. A starter that cranks too slowly or not at all will cause a starting problem. The starter motor or drive mechanism may be bad, or there may be an electrical problem with the starter connections, relay or solenoid. Problems in the ignition switch circuit also may prevent the starter from working.

Required to pass this section of the P2 test:
1. Identify major charging and starting system components.
2. Identify component function and common reasons for replacement.
3. Identify related items such as cables, relays and solenoids.
4. Provide basic use, maintenance, installation, and warranty information.
5. Conduct basic battery tests.


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