What is the anode net charge on a typical AAA battery?

[jaydnul]

I mean on the actually anode, what is the usual net charge around? How many extra electrons to protons are there? The reason I ask is because I'm confused what causes the voltage, is it the higher charge density relative to the other plate?

 

[Evanish]

I'm not that knowledgeable about this so maybe someone will correct me soon, but I don't think there is an excess charge on the plates of a battery. I believe that the current is caused by a redox reaction. Basically chemicals at both plates are reacting with each other. The plates just facility that reaction by transporting electrons from one side to the other.

 

[DrDu]

Evanish is right in that the potential is due to redox reactions, nevertheless there is an excess charge on the plates of the battery.
Specifically, there is a charge double layer on each electrode
http://en.wikipedia.org/wiki/Double_layer_(interfacial)
On a path starting in the electrode and going deep into the electrolyte, the voltage jumps on crossing the double layer on a distance known as the Debye length (see the article) d. I would guess it to be smaller than 1 mum. http://en.wikipedia.org/wiki/Double_layer_(interfacial)
Hence if you know the voltage U of the battery and the surface A of the anode, you can get an estimation of the charge on the anode using formulas for the capacity of a condenser with these dimensions. Namely Q=UC and $C=\epsilon A/d$, where $\epsilon$ is the dielectric constant of the solvent, e.g. of water. So with the assumed Debye length d and A being some cm^2, i would guess C to be about 1 $\mu F$. So Q will be of the order of 1 micro Coulomb.
Without a better knowledge of the Debye length, this is only an educated guess and could be wrong by one or even two orders of magnitude.