1. Definition

Nominal Voltage

Nominal voltage refers to the average operating voltage of a battery under normal conditions. It is a standardized reference value that helps users understand a battery’s expected performance during operation. This value is neither the maximum nor the minimum voltage but represents an approximate midpoint of the battery’s discharge curve.

Different battery chemistries have distinct nominal voltages:

Lithium Iron Phosphate (LiFePO4) batteries: 3.2V per cell

Lithium-ion (Li-ion) batteries: 3.7V per cell

For battery packs, the nominal voltage is calculated by multiplying the nominal voltage of a single cell by the number of cells in series. For example, a 48V LiFePO4 battery typically has a nominal voltage of 51.2V (16 cells × 3.2V).

Nominal Capacity

Nominal capacity indicates the amount of charge a battery can store and deliver under standard test conditions, typically measured in ampere-hours (Ah). It defines how long a battery can supply a certain current before depletion. For instance, a 100Ah battery can theoretically provide 1A of current for 100 hours or 10A for 10 hours.

2. Why Are Nominal Voltage and Nominal Capacity Important?

Nominal values provide a reference for battery selection and performance comparison. They allow users to:

Estimate runtime for specific applications.

Compare batteries of different chemistries and configurations.

Ensure compatibility with electrical systems.

Predict charging and discharging behavior in practical applications.

3. Other Voltage and Capacity Terms

Beyond nominal voltage and capacity, several other key parameters define battery performance:

Operating Voltage (Working Voltage): The actual voltage range during operation, which depends on the battery’s charge level, load, and battery management system (BMS) settings.

Example: A 48V LiFePO4 battery may have an operating voltage range of 43.2V to 58.4V, depending on brand-specific BMS configurations.

Charging Voltage: The voltage required to fully charge the battery. For LiFePO4 cells, this is typically 3.6V per cell, meaning a 48V pack (16 cells) requires a maximum charging voltage of 57.6V to 58.4V.

Discharge Cutoff Voltage: The lowest voltage at which the battery is considered discharged. For LiFePO4 cells, this is typically 2.5V per cell, making a 48V pack’s cutoff voltage around 40V to 43.2V, depending on BMS settings.

Nominal Current: The typical current draw for normal operation, impacting battery longevity and efficiency.

Internal Resistance: The inherent resistance within the battery that affects efficiency, heat generation, and performance. Lower resistance leads to better efficiency and less heat.

4. Common Terminology in Battery Specifications

Manufacturers use different terms to describe battery characteristics, including:

Electrical Performance Parameters – Covers all key electrical specifications.

Electrical Specifications – Defines voltage, capacity, current ratings, and other operational details.

Battery Parameters – Focuses on technical indicators specific to batteries.

Electrical Characteristics – Highlights core electrical properties.

Rated Parameters – Specifies standard values under controlled conditions.

5. Example: 48V LiFePO4 Battery for Golf Carts

A 48V LiFePO4 battery used in golf carts typically has:

Nominal voltage: 51.2V

Operating voltage range: 43.2V – 58.4V (varies by BMS settings)

Charging voltage: ~58.4V

Cutoff voltage: ~43.2V

This provides a stable power supply with long-lasting performance, making it ideal for golf carts that require consistent energy output over extended use.

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A battery is an electrochemical device that produces a voltage potential when placing different metals in acid solutions.The open circuit voltage (OCV) attained varies according to the metals and acid solutions (electrolyte) used.Applying a charge or discharge places the battery in the closed circuit voltage (CCV) condition;charging raises the voltage and discharging lowers it.This voltage behavior is governed by the internal battery resistance;a low resistance produces less fluctuation under load or charge than a high one.

Charging and discharging agitates the battery and a full stabilization takes up to 24 hours.Temperature also has a role;cold rises the voltage and heat lowers it.Manufacturers rate a battery by assigning a nominal voltage and with a few exceptions,these voltages follow an agreed convention.Rating some lithium battery higher than the standard 3.6V/cell may help in product marketing but for the user,a chemistry-specific voltage counts.Here are the nominal voltages of the most common batteries in brief.

Lithium-ion

The nominal voltage of lithium-ion had been 3.60V/cell.This is a practical figure because it represents three nickel-based batteries connected in series (3 x 1.2V = 3.6V). Some cell manufacturers mark their Li-ion products as 3.70V/cell or higher.This poses a marketing advantage because of higher watt-hours on paper (multiplying voltage times current equals W).It also creates unfamiliar references of 11.1V and 14.8V when connecting three and four cells in series.Let this higher voltage not cause confusion; equipment manufacturers will always adhere to the nominal cell voltage of 3.60V for most Li-ion systems,and the standard designation of 10.8V and 14.4V will always work.

The phosphate-based lithium-ion deviates from others in the Li-ion family and the nominal cell voltages are specified at between 3.20 and 3.30V.Because of the voltage difference,the two lithium-ion families are not interchangeable.New lithium 18650 battery will have other voltages and specialty chargers may be needed.

How did this higher voltage creep in?To calculate the nominal voltage,we take a fully charged battery that measures 4.20V and then fully discharge it to 3.00V at a rate of 0.5C while plotting the average voltage.For Li-cobalt,the average voltage comes to 3.6V/cell.Performing the same discharge on a fully charged Li-manganese with a lower internal resistance will result in a higher average voltage.Pure spinel has one of the lowest internal resistances,and the plotted voltage on a load moves up to between 3.70 and 3.80V/cell.This higher midpoint voltage does not change the full-charge and end-of-discharge voltage threshold.

Nickel-based

In consumer applications,NiCd and NiMH are rated at 1.2V/cell,industrial,aviation and military batteries adhere to the original 1.25V.There is no difference between the 1.2V and 1.25V cell;the marking is simply preference.

Primary Batteries

The alkaline delivers 1.5V,silver-oxide 1.6V and primary lithium 3V.The 9-volt battery has six cells in series.Do not charge primary battery because overcharge can produce explosive gases.

Lead Acid

The nominal voltage of lead acid is 2.00 volts per cell,however when measuring the open circuit voltage (OCV),the voltage of a fully charged battery should be 2.10V/cell.Keeping lead acid below 2.10V/cell will cause the buildup of sulfation.