# Does a fully charged battery weigh more than an empty one?

Relevance

not at all!!!!

• Technically - Yes.

A fully charged one has a higher energy state that an empty one. And we now consider mass-energy to be true, where mass and energy is the same thing. Assuming that the chemical energy in the battery can be treated like a mass and weighed then - yes, it is lighter when empty.

But if we are only considering rest-mass of a fully charged battery compared to the rest mass of an empty battery, then no, they both would weigh the same. This is because the high energy electrons that flow out of the battery are replaced by low energy electrons. So the rest mass stays the same, but the energy content is lower.

Hope that helps.

• In principle, the fully charged battery should weigh more because it contains more energy, and the same amount of matter. However, as in all chemical processes, the mass change is unmeasurably small because

E = mc^2

and c is a large number.

The fact that this is potential energy is beside the point. Nuclear energy is also potential energy, but the energy differences are large enough to cause measurable differences in mass.

• Yes but!

weight of a fully charged battery

=

total mass * g = g * (E "charged")/c^2 + (mass of uncharged battery)

where g=9.8 m/s^2

but the mass equivalent put in by charging: (E "charged")/c^2

can be thrown out the window! Forget it!

real batteries loose water,gas,etc. molecules per

unit time. These actions result in the battery having

a net loss of mass over time.

• No, they weigh the same, the mass is the same. Charging a battery reconfigures the way the atoms combine, and how the electrons are configured, but it is, after all, the same stuff in the battery: the same atoms and molecules; the same number of electrons, protons, and neutrons. The potential energy is different, but if you lifted an object into the air, the potential energy would be different, but you would not expect it to change its weight or its mass.

This involves, of course, changes at the electromagnetic level. it does not involve changes at the level of the nucleus: neither the strong nor weak forces are involved, and so for all but the most abstract theoretical consideration, one can discount any energy to mass equivalency.

• Since charging a battery normally involves the release of H2, that mass escapes and reduces the mass of the battery and ergo its weight.

Source(s): MHO
• I have never thought about that before - Great question! I don't know the answer but I'm kinda thinking that since it has greater energy it must have greater mass (A tiny bit greater).

I look forward to see what others say.

• Anonymous