IANAS, so I thought I’d give a theory a try…
My theory is that charging a battery involves taking electrons from a wall and putting them in the battery (via a chemical reaction). When you use a battery, said electrons go from the battery to the appliance. Electrons have mass, and there are a lot of electrons in a battery. Obviously, there is no perceptible difference in AA’s, but what about something like a UPS for a computer?
Compared to protons and neutrons, electrons don’t weigh that much at all. The difference in weight between a fully charged and fully dis-charged battery is only the relative weight of a few molecules, if that.
nope, you are just moving electrons around from one electrode to the other. As you charge or discharge a battery. the same current which enters via one wire exits via the other. You cannot charge or discharge a batteery with only one wire.
scratching head
I thought that batteries used the concept of reversible chemical reactions…
Li --> Li[sup]+[/sup] + energy (and vice versa)
I don’t understand what you mean by passing current through electrodes. I guess I don’t understand how a battery charges then…
Not to go into it, but I believe you’ve written a half-equation that would happen at one electrode. At the other, the electron would join another substance to form a lower energy molecule.
For example, in a lead-acid battery the equation is:
Pb + PbO2 + 2H+ 2HSO4 => 2PbSO4 + 2H2O + 2e-
The electrons don’t accumulate in the appliance- they “move” down their potential through the appliance, performing work, and returning to the opposite electrode.
Check this site for the basics on batteries.
They do loose energy which is equivalent to mass, so they may be lighter by that miniscule amount.
PC
I always find it helpful to think of electricity in terms of a water power analogy. Think of electrons as water. In the charged battery, the water is all at the top of the hill. As it discharges, the water runs downhill, driving a waterwheel that does work. When it’s dead, all the water is at the bottom of the hill. Recharging it is like running a water pump to get it back up.
It the energy that moves, not necessarily the electrons.
zink-air batts will change mass are they are used (as air (02?) is a component added. Also older unsealed lead acid batt’s give off gas so their mass changes.
the others really don’t change as electrons from one side are transfered to the other (they might not be the same electorns however, but one electron is as good and another).
If you go to the mass = energy level then a charging batt is gaining mass via E=mc^2
And in case you’re wondering what ‘miniscule’ amounts of mass due to energy differences are:
My quick and not-double-checked calculation using E=mc-squared shows an AA battery with a capacity of 2,500 mA-hours will lose about 0.00000000015 grams as it’s discharged. This is just because the potential energy in the battery carries with it some mass - a miniscule amount to be sure, but there. It will of course gain that mass back as the energy is put back in during recharging.
Of course, I wouldn’t be surprised if you lost or gained much more than that by scraping the contacts as you put the battery in the charger. So actually measuring this effect with your bathroom scale could be difficult…
Also I have been looking into getting rechargable nimh batts. It seems like all manufactured are claiming better life then alkalines (on a single charge).
Now I have experence w/ nicd batts w/ their apx 600mah rating and know that alks will easilly outlast them in all but the most draining equipment (due to nicd low internal resistance) But can I really expect longer run times with nimh in items like 2 way radios, cd player and gps?