Are charged batteries heavier than dead ones?

[Carsinmyblood]

I told a friend about the impending Mach E purchase and the discussion turned to electric planes and eventual passenger jets without the jets, of course.

He said something that I couldn't dispute. He said batteries get lighter as they discharge. I didn't want to appear un or misinformed.

So, DO batteries change their weight? Even slightly?

Turns out he was right. It's almost immeasurable though, so put away your bathroom scales. Mathematically, energy has mass. Learned something new today.

https://physics.stackexchange.com/q...s-of-a-battery-change-when-charged-discharged

Sponsored

 

[ChasingCoral]

I told a friend about the impending Mach E purchase and the discussion turned to electric planes and eventual passenger jets without the jets, of course.

He said something that I couldn't dispute. He said batteries get lighter as they discharge. I didn't want to appear un or misinformed.

So, DO batteries change their weight? Even slightly?

Turns out he was right. It's almost immeasurable though, so put away your bathroom scales. Mathematically, energy has mass. Learned something new today.

https://physics.stackexchange.com/q...s-of-a-battery-change-when-charged-discharged

Maybe that's why the GOM is often wrong. Did Ford forget to take battery mass change into account? ?

 

[dml105]

I told a friend about the impending Mach E purchase and the discussion turned to electric planes and eventual passenger jets without the jets, of course.

He said something that I couldn't dispute. He said batteries get lighter as they discharge. I didn't want to appear un or misinformed.

So, DO batteries change their weight? Even slightly?

Turns out he was right. It's almost immeasurable though, so put away your bathroom scales. Mathematically, energy has mass. Learned something new today.

https://physics.stackexchange.com/q...s-of-a-battery-change-when-charged-discharged

The amount your battery changes in mass when charged versus uncharged is immeasurably small. The difference in weight of your Mach-e when in the rain vs. on a dry sunny day is greater than the difference weight of your Mach-e when charged versus discharged.


I like to think of the battery as a giant rubber band. Like in the wooden toy cars that run on rubber bands! It takes energy to wind your rubber band, and the controlled release of the band can drive the toy car forward. But the mass of the rubber band doesn’t change.

Same with your battery - charging it moves electrons from a resting state to a charged state where they really don’t want to be. The motors allow them to move to where they DO want to be, but they gotta pay the toll first - propelling the car forward as the move.

This is one of the major hurdles against battery powered planes. A jet propels by tossing mass out the back, and as a result, the jet gets lighter as it travels. Batteries don’t toss mass and get measurably lighter, so the best they can be used for is to turn a propeller. What’s old is new again!

 

[ZuleMME]

Technically E = ±mc^2 . Solve for M... you'll see that energy does have mass, but the speed of light being involved in the calculation shows you the infinitesimally small nature of it. Suffice to say a fly landing on your car has more impact than your charge level.

 

[dml105]

Technically E = ±mc^2 . Solve for M... you'll see that energy does have mass, but the speed of light being involved in the calculation shows you the infinitesimally small nature of it. Suffice to say a fly landing on your car has more impact than your charge level.

Using E=mc^2 assumes the electrons are being consumed (converted into energy), but they’re not. They’re just moving from one place in the battery to another. The energy consumed is the return of potential energy put into the battery by the charger.

 

[ZuleMME]

Using E=mc^2 assumes the electrons are being consumed (converted into energy), but they’re not. They’re just moving from one place in the battery to another. The energy consumed is the return of potential energy put into the battery by the charger.

Perhaps you should read the article linked above. We're talking energy stored in potential here, that's right, energy itself. Not the matter. But suffice to say a TINY amount of matter is consumed in the process of discharge (his reference case was calclated at half a microgram) and replaced in the process of charging due to the weight of the atoms being chemically altered.

 

[dml105]

Perhaps you should read the article linked above. We're talking energy stored in potential here, that's right, energy itself. Not the matter. But suffice to say a TINY amount of matter is consumed in the process of discharge (his reference case was calclated at half a microgram) and replaced in the process of charging due to the weight of the atoms being chemically altered.

I did read the article. We are in agreement through this section:

So we will continue with the scenario II in which the atoms inside the battery are only rearranged into different configurations or different molecules but the identity and the number of the nuclei inside the battery is constant.

Let me just emphasize that the energy can't be calculated from masses of the electrons. Electrons are not lost when a battery is discharged. If a battery is losing electric energy, it doesn't mean that it's losing the electric charge! They're just moved from one electrode closer to the other and it's just the motion through the wire stretched between the electrodes (and the electric field inside the wires) that powers the electric devices. But the whole battery is always electrically neutral; because it contains a fixed number of protons, it must contain a fixed (the same) number of electrons, too.

Instead, the energy difference really boils down to different electrostatic potential energies of the electrons relatively to the nuclei. One could say that when a battery is being discharged, its electrons are moving to places that are closer to the nuclei, perhaps other nuclei, in average and the modified interaction energy affects the amount of energy=mass stored in the electromagnetic field.

Then he goes a bit off the rails by measuring the mass-equivalent of the 16 kWh stored in a Volt battery anyway, contradicting what he had just said. (Yes, I'm disagreeing with a Harvard professor. Not my first time.) But he does eventually agree - the change in mass is not measurable.

It is incorrect to say a tiny amount of mass is consumed. The number of electrons in a battery is the same charged or discharged.

 

[ZuleMME]

It's the atomic weight changing I should say, not being consumed. The Lithium changes it's partner/molecular formation during the process of charging/discharging.

 

[RonTCat]

Mass is not weight... maybe a fully charged battery creates a magnetic field when discharging, and it's in opposition to the earth's field... your car may want to float away...lol...

 

[Carsinmyblood]

It would be a simple experiment requiring no calculation of weight at all with identical batteries. Put a discharged battery and a fully charged battery on opposing sides of a balance beam. Now, charge the dead battery with the full one til they match charges.

I'd love to find that, surely someone with access to a lab has done it.

 

[GoGoGadgetMachE]

Mass is not weight... maybe a fully charged battery creates a magnetic field when discharging, and it's in opposition to the earth's field... your car may want to float away...lol...

finally, the flying cars we were promised!

 

[RonTCat]

I did read the article. We are in agreement through this section:


Then he goes a bit off the rails by measuring the mass-equivalent of the 16 kWh stored in a Volt battery anyway, contradicting what he had just said. (Yes, I'm disagreeing with a Harvard professor. Not my first time.) But he does eventually agree - the change in mass is not measurable.

It is incorrect to say a tiny amount of mass is consumed. The number of electrons in a battery is the same charged or discharged.

To make the battery heavier, just take off the positive cable when charging. That's where all the electrons are leaking out.

OK, I'll show myself out...

 

[Jimrpa]

May I introduce you to the Ford Nucleon? ? Everyone forgets that Ford has a LONG history of research into alternative fuel vehicles ?

 

[dml105]

^^^

Yes. Though I would say "nuclear reactor," instead of bomb. More polite.

Sponsored