Understanding Battery Voltages and Charging Requirements: A Comprehensive Guide

Batteries vary in the number and voltage of their cells. There is no restriction and no such thing as a 'universal' charger. Commonly used battery voltages like 12 volts are widespread because they are ideal for many applications, such as in cars and charging systems. However, it is crucial to understand the underlying principles to ensure safe and efficient charging.

Why Do We Use 12 Volt Batteries?

12 volt batteries are very common due to their versatility and standardization in low voltage DC applications. They are particularly prevalent in automotive uses, such as cars, and have become a de facto standard. However, this does not mean that 12 volt batteries should be charged with a 12 volt supply. For instance, you cannot charge a nominal 12 volt battery with a 12 volt supply. Instead, a higher voltage supply (more than 15 volts) is always required to charge a fully charged 12 volt battery to its peak.

The Chemistry Behind Battery Voltages

The voltage of a battery depends on the chemistry of the battery. Different chemistries produce different voltages and characteristics. Here are some examples:

Lead Acid Batteries: These common batteries have a cell voltage of about 2 volts. A car or UPS (Uninterruptible Power Supply) battery typically has 6 cells wired in series, resulting in a nominal 12 volt battery. The precise voltage fluctuates based on the state of charge. A fully charged lead-acid battery is approximately 12.7 volts, dropping to about 12 volts when fully discharged. Lithium Batteries: These have a cell voltage of about 3.7 volts and are used in modern portable electronics and power tools. NiMH (Nickel-Metal Hydride) Batteries: These have a cell voltage of 1.25 volts and are used in flashlights and cameras. Alkaline Batteries: They have a cell voltage of 1.5 volts and are used in a wide range of devices, from radios to remote controls.

Sother Historical Context and Trends

Before the 1960s, 6 volt batteries were just as common as 12 volts, especially in Euro cars with smaller engines. Today, modern electric cars use voltages over 400 volts DC for their drive systems and a lower 12 volts for auxiliary functions like lighting and computers. Some car manufacturers are experimenting with 48 volts for the 'other stuff' in future models. Additionally, big trucks have used 24 volts for starting for many years. Airplanes, on the other hand, use 400Hz AC for various purposes, but the specific voltage can vary.

Charging Voltages and Electrical Systems

In a car's electrical system, even though the battery is labeled as 12 volts, it typically operates at about 14 to 14.5 volts most of the time due to the alternator constantly charging it. To begin charging, the voltage must reach about 14 volts. Once the car's motor stops, the battery voltage would drop to almost 10.8 volts, which is considered completely discharged (fully charged being around 13.8 volts).

High Voltage Safety

The threshold for "high voltage" is generally 60 volts. Voltages above this often require stricter, more expensive safety measures, such as specialized connectors and cables designed for high voltage systems. This is particularly important in electric vehicles and aircraft.

Understanding these principles is crucial for anyone involved in battery maintenance, charging, and system design. Whether you are a hobbyist, an automotive technician, or an electrical engineer, grasping the fundamentals of battery voltage and charging requirements is essential to ensure safe and efficient performance.