Boondocker, Glenn offers the source code for the PicAxe and the associated logging-software. It is refreshing just how well written and simple his code is. The voltage divider provides a safe(0-5volt) input to the PicAxe, which is then digitized to 10-bit-resolution. The software does the math to convert this back to the real analog battery voltage of 0-12volts.
This little chip is meant for elementary learning, but proves as a very useful and flexible tool.
Cheers!