Batteries vs. Alternators: Understanding Voltage Drops


Batteries and alternators are two important components in a vehicle's electrical system. Both play a crucial role in powering the vehicle, but they work in different ways and serve different purposes. In this blog post, we will explore the differences between batteries and alternators and why voltage drops can occur.

Section 1: Batteries

What is a Battery?

A battery is a device that stores electrical energy and provides a source of power to a vehicle's electrical system. The battery is typically located in the engine compartment and is responsible for starting the engine. Once the engine is running, the alternator takes over the responsibility of powering the vehicle's electrical system.

How Does a Battery Work?

A battery has a series of cells that convert chemical energy into electrical energy. The most common type of battery used in vehicles is a lead-acid battery, which consists of lead plates and an electrolyte solution of sulfuric acid. When the battery is charged, the lead plates are covered with lead sulfate, which acts as an insulator. When the battery is discharged, the lead sulfate is converted back into lead and sulfuric acid, releasing energy in the process.

Section 2: Alternators

What is an Alternator?

An alternator is a device that generates electrical power while the engine is running. The alternator is typically located on the front of the engine and is connected to the engine by a belt. The alternator is responsible for powering the vehicle's electrical system once the engine is running.

How Does an Alternator Work?

An alternator works by converting mechanical energy into electrical energy. This is done by spinning a rotating magnetic field inside a stationary set of coils. The rotating magnetic field induces a current in the coils, which is then rectified and used to power the vehicle's electrical system.

Why Voltage Drops

Both batteries and alternators are important components of a vehicle's electrical system, but voltage drops can occur, which can cause problems for the vehicle. Voltage drops occur when there is a decrease in the voltage supplied by the battery or alternator. This can happen for a variety of reasons, including a failing alternator, a weak battery, or a problem with the electrical system.

Failing Alternator

A failing alternator can cause a voltage drop because it is no longer able to generate the necessary electrical power to power the vehicle's electrical system. This can happen if the alternator is not functioning correctly, or if the belt that drives the alternator is worn or broken. If the alternator is not functioning correctly, the battery will have to pick up the slack and provide more power, which can cause the battery to discharge faster.

Weak Battery

A weak battery can also cause a voltage drop. This can happen if the battery is old or has been damaged. A weak battery may not be able to supply enough power to the vehicle's electrical system, which can cause the voltage to drop.

Problem with the Electrical System

Problems with the electrical system can also cause voltage drops. This can happen if there is a loose or corroded connection in the electrical system, or if there is a problem with the wiring. These issues can result in a decrease in the voltage supplied by the battery or alternator, causing a voltage drop.


In conclusion, batteries and alternators are essential components in a vehicle's electrical system, but voltage drops can occur for various reasons. Understanding the differences between batteries and alternators, and the causes of voltage drops, can help you troubleshoot and prevent problems with your vehicle's electrical system. Regular maintenance and inspections can help ensure that your battery and alternator are functioning properly and help prevent voltage drops from occurring. Robert Kerns Explains Alternator power vs Battery power in this video:"