# Absolute voltage values at battery terminals

• klng
In summary, when a battery is rated at 3 volts, there is potential difference of 3 volts across the +ve and -ve ends of the battery.
klng
Hi all,

Lets say i have a battery with a rated voltage of 3V. This means that there is a potential difference of 3 V across the +ve and -ve ends of the battery. This can mean 3V/0V, 5V/2V, 6V/3V and the list of possible combinations goes on.

My question:
Is there any way of knowing the absolute voltage values at the +ve and -ve terminals of the battery? Can we safely take it that the -ve terminal is at ground potential (i.e. at 0V)?

There is -by definition- no such thing as "absolute voltage".
Voltage is just a measure of potential energy and as you know there is no such thing as "absolute" potential energy: the value of the gravitational potential energy of a ball on a table depends on if you calculate it with respect to the floor or the moon.
The same thing is true for voltage.
The point is that it is the difference that matters.

Can we safely take it that the -ve terminal is at ground potential (i.e. at 0V)?

absolutely NOT: you can ground the positive terminal or the negative terminal...it's all relative. further, if neither is grounded via a connection it's likely the voltage will vary over time relative to ground while maintaining the 3 volt difference your note. Grounding is a potentially complex and interesting subject rarely dealt with in undergraduate studies.

I can't think of any circuits that are normally positive ground...some boat dc (battery) circuits were made that way until maybe the 19030's or early 1940's but it was discovered they were more susceptible to corrosion so as far as I know all such marine circuits are negative ground today.

Are car alternators ALL negative ground now?? Some used to be positive...I do not know what the current stabndard is. GM,Detroit Diesel and Ford have been negative ground for a long time...

Thank you both for the wonderful and insightful replies.

## 1. What are absolute voltage values at battery terminals?

Absolute voltage values at battery terminals refer to the exact measurement of the electrical potential difference between the positive and negative terminals of a battery. It is measured in volts and indicates the strength of the battery's electrical charge.

## 2. How are absolute voltage values at battery terminals measured?

Absolute voltage values at battery terminals are typically measured using a voltmeter, which is a device that can accurately measure the voltage of a battery or any other electrical source. The voltmeter is connected to the positive and negative terminals of the battery to obtain the voltage reading.

## 3. Why are absolute voltage values at battery terminals important?

Absolute voltage values at battery terminals are important because they provide crucial information about the health and performance of the battery. It helps determine if the battery is fully charged, partially charged, or completely drained. It is also important for ensuring the proper functioning of electrical devices powered by the battery.

## 4. What is the ideal absolute voltage value for a battery?

The ideal absolute voltage value for a battery depends on its type and size. Generally, a fully charged lead-acid battery will have an absolute voltage value of around 12.6 volts, while a fully charged lithium-ion battery will have an absolute voltage value of around 4.2 volts. It is important to refer to the manufacturer's specifications for the ideal voltage values for a specific battery.

## 5. Can absolute voltage values at battery terminals change over time?

Yes, absolute voltage values at battery terminals can change over time. This is because batteries gradually lose their charge over time, resulting in a decrease in voltage. Factors such as temperature, usage, and age can also affect the voltage values of a battery. Regularly checking and maintaining the battery can help prevent significant changes in absolute voltage values.

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