It may be me but I have noticed that when my mobile phone is fully charged it weights more than when the battery is flat.

What is going on?

Never realized

huh ? its just your feeling i guess

Get a kitchen scale and actually weigh it and find out if you're going nuts or not. haha.

I agree. It must be psychological. you think the phone must be heavier because its' battery is full.

You know what, you are right, sometimes it feels like old batteries are lighter than new ones, but that could be (for me) different models.

I looked around and got conflicting info and couldn't find a good source. My gut says it must lose some mass through it's energy output but at the same time I'm not sure. Either way the amount of electrons in a battery are on the order of a billionth of an ounce so if you can feel the difference between that your super sensitive!

I can't think of any practical reason why the battery would weigh more when it's fully charged - nothing is entering or leaving the battery other than electrons, which as capeo pointed out are of negligible mass. Unless you find a scale returns different weights, I'd say it's psychological.

some total guesstimations here, this figure is probably WAY over the real figure.

Lets say it runs on 12 volts and 12 amps, and goes 24 hours between charges.

This means it puts out 12*12 = 144 watts of energy. A watt is a joule per second. 144* 60*60*24 = 12441600 joules (kg M^2 / s^2) used up in 24 hours between chargings. Now I KNOW I overestimated the energy - if it really used this much electricity it would be putting out more heat than a 100 watt lightbulb, or even an entire human body.

Now we use E=MC^2 to figure out the mass increase from 12441600 joules

M = E/(C^2)

M = 12441600 (kg m^2 / s^2) / ((300,000,000 m/s)^2)

M = 0.00000000013824 kg, or 0.00000013824 grams, and thats INCLUDING my wild overestimations. It's your imagination.

And NO, there are NOT any more electrons in the battery when it is charged than when it isn't. The only difference is that when it is charged certain chemical reactions happen in the reverse order than they happen when the battery is putting out energy, taking the flow of electrons and transforming their kinetic energy into chemical energy.

Just injecting a little math! You can figure out so many things with a little physics.

No, must just your imagination, no scale is going to be able to measure the difference between charged and uncharged...

Are you saying that you weighed it before and after, or are you saying it feels heavier?

Except you don't apply the equation for photons to electrons.

I don't understand what you're trying to say. A watt is a measure of energy per unit time. It does not matter what form that energy is in. Light (each photon carrying an energy) at a certain intensity (photons per second) can carry a watt. A certain voltage (equivalent to energy per electron) multiplied by an amperage (electrons passing through per second) can carry exactly the same energy. Photons don't really enter into this discussion.

Oh this....Must have messed up my equations, physics exam or whatever. You're right, photons don't enter into the equation. Still, I don't see what it's for, it's nigh impossible for him to charge a battery enough for a significant change of mass to occur.

Unless it was a NUCLEAR battery...

I didn't weigh the phone charged and uncharged I simply thought it felt lighter.

If gravity and elecromagnestism can be unified as scientists suspect then surely one must effect the other.

Feeling the weight of something at two different times is quite subjective. I actually thought about this walking around campus the last few days and I've found that my phone feels heavier to me when cold than hot. To anticipate an argument: to a degree way greater than can be explained by displacement of air, that's negligable.

the E=MC^2 mass is the only thing that can affect the mass of a battery in the way described. And even if electromagnetic fields somehow effected gravity, there is NOTHING special about the electromagnetic field of a battery. It is an inert lump of chemicals when it is not in use. All that happens is when you close the circuit, electrons can pass out one contact of the battery through the device into another because near one contact a reaction happens that produces electrons and positive ions, and near the other a reaction happens that requires positive ions and electrons (and the electrons are blocked from traveling through the battery itself). And when IN use there is only an equal current in the battery to the rest of the device. People think of electricity as some kind of strange magical thing when it is really just the movement of electrical charges. In a battery it is just electrons moving to a place where they are more tightly bound through a wire. It's that simple.

<end of rant> haha sorry I can go on and on about these things ... when I get on a science topic I go on and on and on and have a tendency to sound like I'm calling other people stupid when I'm not.

this topic feels like science class ...

Forget gravity. What about human receptors? Charging a battery....doesn't it release free radicals?