In one of the answers on this site, I found link to this project. That article mentions internal resistance of batteries and cells. Where can I find data about common ranges of internal resistances for batteries? I've always heard that it's low, but I couldn't find anywhere how low is low and common resistances for common battery types.
For example, here is the datasheet for Duracell Plus AA (retail) batteries: http://www.farnell.com/datasheets/97133.pdf
If you do some searching around on the websites of Duracell, Energizer and the like you can often find these datasheets, though they are hidden away. I found this on Farnell's website.
First page, table 1: "Nominal Internal Impedence" - 181mohm @ 1kHz.
A standard alkaline Energizer AA battery has an internal series resistance of 150 to 300 milliohms, from the datasheet here. The asterisk by that number will refer you to Energizer's whitepaper on battery internal resistance.
Take some time to look around data.energizer.com, it's really a very good resource.