Identifying the Negative Battery Terminal: A Comprehensive Guide

Battery terminals are the critical points for connecting and disconnecting a battery from a vehicle or other devices. Correctly identifying the positive and negative terminals can prevent damage to your equipment and ensure safe operation. This guide will help you identify the negative battery terminal, especially when the polarity signs are obscured or worn away.

Common Indicators of Negative Terminals

Traditionally, the negative terminal is the smaller of the two terminals. It may also have a “-” sign, or be marked “-” or ” ” on the opposite terminal. Signs can be obscured or worn away over time. For instance, in General Motors (GM) batteries, both terminals are usually the same size, which can make identification more challenging.

Diagnostic Methods

To identify the negative terminal accurately, a multi-function digital volt/ohmmeter (DVM) is highly recommended. Here’s a step-by-step guide on how to use a six-function DVM to identify the terminals:

Using a Multi-Function DVM

Set the DVM to Volts/Ohms with the red lead connected to the Volts/Ohms setting and the black lead connected to the common setting. Place the black lead on the negative terminal. The display will read the voltage. Switch the red lead to the terminal opposite the one connected with the black lead. If the display shows no “-” sign, the black lead was correctly placed on the negative terminal.

Note: Be cautious with very old lead acid batteries, as they can reverse. If the display shows the opposite polarity (a “-” sign), ensure you reverse the leads.

A Quick and Dirty Method

If you have a battery that is the correct size for a car, you can use this simple test. Insert the battery into the battery box. Typically, the negative terminal connects to the chassis, which will reach the negative post but not the positive post. The same applies to the positive cable, which usually connects to the starter and solenoid, reaching only the positive terminal.

General Observations

Each battery has two metal terminals - one marked positive ( ) and one marked negative (-). However, many batteries are not marked with polarity signs. In these cases, the negative terminal is typically the smaller one and is always marked with a “-” sign, while the positive terminal is marked with a “ ” sign (if present).

Some battery types, such as AA, AAA, D, C, and other round or long-shaped batteries, do not have any markings or at best a “ ” sign at one end. However, most people recognize the small nibble or raised mark at one end as the positive terminal ( ) and the larger flat end as the negative terminal (-).

Most car batteries have both terminals marked with the same post, so a label is crucial for identification. Identifying the negative terminal is crucial, especially in older British cars with positive grounding, where the negative terminal typically connects to the chassis (bodywork) rather than additional electrical components.

Conclusion

Identifying the negative terminal is a critical step in safely working with batteries. By using the provided methods, you can accurately identify the negative terminal even if the polarity signs are obscured or worn away.