Battery Voltage – Battery Education

What is battery voltage? I think we talk around the real definition so much we actually begin to believe that we understand what it means when in reality we do not. Even I was just commenting to my wife that I wish I paid more attention while I was in my college electronic classes so that I too could understand the very basics of voltage . For my benefit as well as yours let us go back to the basics of what battery voltage really means and how the work it conducts inside your battery affects the other technical factors of your battery.

Italian physicist Alessandro Giuseppe Antonio Anastasio Volta (February 18, 1745 – March 5, 1827) grew up with a passion for electricity. In 1775 he devised the electrophorus, a device that produced a static electric charge. In 1776-77 he studied the chemistry of gases, discovered methane, and devised experiments such as the ignition of gases by an electric spark in a closed vessel.

In 1800 he developed the voltaic pile, a forerunner of the electric battery, which produced a steady electric current. Creating a cell, a wine goblet filled with brine into which the two dissimilar electrodes were dipped, Volta placed together several pairs of alternating copper (or silver) and zinc discs separated by cloth and soaked the cloth in brine (salt water) to increase conductivity, and an electrical current was produced. The electric pile ultimately replaced the goblets with cardboard soaked in brine. The number of cells, and thus the voltage the electric pile could produce, was limited by the pressure, and exerted by the upper cells that would squeeze all of the brine out of the cardboard of the bottom cell.The electric pile was the first electric battery.

In 1881 the electrical unit we know today, the volt, was named in Volta’s honor. From the first battery, mentioned above, we can derive a definition of voltage as: Volts – or V – are an electrical measure of energy potential. Voltage can also be thought of as the amount of "pressure" of electrons that pass from a negative connector to a positive connector. Or V can be defined as the measure of the strength of an electrical source of power for a given current level.

Voltage can also be defined as Electrical Potential difference – a quantity in physics related to the amount of energy that would be required to move an object from one place to another against various types of force. In the fields of electronics the electrical potential difference is the amount of work per charge needed to move electric charge from the second point to the first, or equivalently, the amount of work that unit charge flowing from the first point to the second can perform.

Mathematically voltage is commonly measured by V= I x R; where V=Voltage, I=Current, R=Resistance.

Beyond the definition what challenges many is the confusion that a battery contains four unique types of voltage measurements. Each voltage measurement type residing in a battery effects battery life.

Float Voltage – is battery voltage at zero current (with battery disconnected).
Nominal Voltage – is battery voltage range 3.7V, 5.2V, 10.2V, 12V etc that says that a voltage range exists depending on the number of cells in the battery. For example a 12 Volt battery is made of 6 cells and has a Float voltage of about 12V.
Charge Voltage – The voltage of a battery while charging.
Discharge Voltage – The voltage of a battery while discharging. Again, this voltage is determined by the charge state and the current flowing in the battery.

Here are a few examples of how the voltage types measurments interact with one another in the same battery:

Number of Cells	Nominal Voltage	Fully-Charged Float Voltage	Fully-Discharged Float Voltage	Discharge Voltage at Ah/20	Charge Voltage at Ah/5
1	2	2.15	1.9	2.0 – 1.7	2.1 – 2.30
6	12	12.9	11.4	12 – 10.2	12.6 – 13.8
12	24	25.8	22.8	24 – 20.4	25.2 – 27.6