Weight difference between a charge and discharged battery

In summary: Assuming an a suitably accurate weighing device...The weight of a battery decreases after it is depleted, due to the loss of internal energy.
  • #36
leothorn said:
Do the conclusions of then discussion hold if the concept of mass in special relativity does not hold ? ( A contention held at the end of the article linked above ?
It was just saying that some people think the definition of 'relativistic mass' is not very useful. They are not saying it is wrong.

leothorn said:
When the battery system is at higher energy that is the constituent particles are at higher state of activation, they hit the confines of the battery at a much faster rate than when the battery is at lower energy. The combined affect of higher average impulse over time should affect the weight of the battery.
As Nugatory said, the molecules won't necessarily be moving around faster. Remember that the molecules have more than just kinetic energy. They also have 'chemical energy', which is energy stored in the electromagnetic field. And it is this chemical energy that changes, to provide the energy to the circuit.

Now, if you want to talk about what happens when we place the battery in a gravitational field, then put it on a scale... Well, the mass of the molecules is greater in the high-energy state. So it makes sense that the battery will then push down more on the scales when its molecules are in the high-energy state.

I guess the last 'connection' to make is that the mass of the molecules of an object effect the mass of the object. But this is classical physics. There is no relativistic argument required here.

edit: more explanation: I can see why (for fluids), it is not obvious why the mass of the molecules should affect how much the battery pushes down on the scales. But if you think of the pressure created by these molecules, the pressure will be greater when the molecules are more massive.
 
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  • #37
Yes there would be a weight difference. The charged battery would weigh* more. All energy** gravitates.

*here the working definition of weight, is what you measure on a scale

**gravitational energy is a concept only useful in certain limits, and does not apply here.
 
  • #38
Thanks, Nugatory! I think this is making more sense to me, now.

So am I getting this right? Light does not have a rest mass itself, but it can increase the rest mass of systems it is contained in?
 
  • #39
a single photon cannot have rest mass. A collection of more than one photon can.
 
  • #40
There is a key aspect of batteries that seems to have been overlooked:

The easiest way to think about what is happening in the battery to start with Drakkith's comments. In addition what needs to be explicitly mentioned is that no battery is an ideal power source: all batteries have internal resistance. That is where chemical energy lost during discharge is converted to heat energy, or mass equivalent losses if you prefer.

So when chemical reactions take place in the battery, chemical potential energy* is dissipated and this partially appears within the battery as heat [i2R losses where R is the internal resistance of the battery]. Most power is delivered to the external circuitry. So Nugatory's quick power loss calculation [post #11 I think] has the right idea regarding energy/mass-equivalent loss, but some of that loss IS within the battery.

edit: * As Bruce noted: ..." 'chemical energy'... is energy stored in the electromagnetic field" of the battery components. Charging and discharging changes the chemical composition of the battery plates.

[For example some 20% of the power delivered by a wet cell lead acid battery [like a car battery] is dissipated via its own internal resistance losses, and conversely when charging, some 20% of the charge power is lost in internal heating. So you cannot charge them too fast or they will overheat [boil off electrolyte] ...not above about 20% of their rated amp hours. In contrast, an AGM [absorbed glass mat] battery, for example, has very low internal resistance, so heating is not much of an issue: they can be charged at 100% of their rated amp hour capacity and in charging and discharging only a few percent of power is lost to internal heating..about 2% or 3% as I recall. ] So an AGM battery offers significantly higher efficiency [at significantly higher cost].]

Light does not have a rest mass itself, but it can increase the rest mass of systems it is contained in?

yes.
The photon has the equivalent of 'mass' via it's energy content E = hf. So when an atom absorbs a photon, typically an orbital electron might be bumped to a higher energy level. So now the atom has stored some additional energy and via E = mc2 it has a tad more equivalent mass...but that is stored as energy.

photon energy relationships described here:

http://en.wikipedia.org/wiki/Photon_energy#Physical_properties
 
Last edited:
<h2>1. What causes the weight difference between a charged and discharged battery?</h2><p>The weight difference between a charged and discharged battery is primarily due to the movement of ions within the battery. When a battery is charged, ions move from the positive electrode to the negative electrode, causing an increase in weight. When the battery is discharged, the opposite occurs and ions move from the negative electrode to the positive electrode, resulting in a decrease in weight.</p><h2>2. How significant is the weight difference between a charged and discharged battery?</h2><p>The weight difference between a charged and discharged battery is relatively small, usually only a few grams. However, this can vary depending on the type and size of the battery. For example, a small button cell battery may only have a weight difference of a few milligrams, while a larger car battery may have a weight difference of several kilograms.</p><h2>3. Does the weight difference between a charged and discharged battery affect its performance?</h2><p>No, the weight difference between a charged and discharged battery does not affect its performance. The movement of ions and resulting weight difference is a normal part of the battery's functioning and does not impact its ability to store and release energy.</p><h2>4. Can the weight difference between a charged and discharged battery be used to determine its charge level?</h2><p>No, the weight difference between a charged and discharged battery cannot be used to accurately determine its charge level. While a charged battery will have a slightly higher weight than a discharged battery, this difference is too small to be measured without specialized equipment. It is best to use a battery tester or monitor the battery's voltage to determine its charge level.</p><h2>5. Does the weight difference between a charged and discharged battery change over time?</h2><p>Yes, the weight difference between a charged and discharged battery can change over time due to factors such as the battery's age, usage, and storage conditions. As a battery is used and recharged, its weight difference may become less noticeable. Additionally, a battery's weight difference may also be affected by factors such as temperature and humidity.</p>

1. What causes the weight difference between a charged and discharged battery?

The weight difference between a charged and discharged battery is primarily due to the movement of ions within the battery. When a battery is charged, ions move from the positive electrode to the negative electrode, causing an increase in weight. When the battery is discharged, the opposite occurs and ions move from the negative electrode to the positive electrode, resulting in a decrease in weight.

2. How significant is the weight difference between a charged and discharged battery?

The weight difference between a charged and discharged battery is relatively small, usually only a few grams. However, this can vary depending on the type and size of the battery. For example, a small button cell battery may only have a weight difference of a few milligrams, while a larger car battery may have a weight difference of several kilograms.

3. Does the weight difference between a charged and discharged battery affect its performance?

No, the weight difference between a charged and discharged battery does not affect its performance. The movement of ions and resulting weight difference is a normal part of the battery's functioning and does not impact its ability to store and release energy.

4. Can the weight difference between a charged and discharged battery be used to determine its charge level?

No, the weight difference between a charged and discharged battery cannot be used to accurately determine its charge level. While a charged battery will have a slightly higher weight than a discharged battery, this difference is too small to be measured without specialized equipment. It is best to use a battery tester or monitor the battery's voltage to determine its charge level.

5. Does the weight difference between a charged and discharged battery change over time?

Yes, the weight difference between a charged and discharged battery can change over time due to factors such as the battery's age, usage, and storage conditions. As a battery is used and recharged, its weight difference may become less noticeable. Additionally, a battery's weight difference may also be affected by factors such as temperature and humidity.

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