gardner:
You could make the ground leg of the voltage divider be an Arduino output pin. Make it low to assert ground, take your A2D measurement, then make it an input and write a 0 to it, to turn off the pull-up. It should not sink much current in this state.
The measurement is from the voltage divider (battery's 9V pole) to A1, and the switch is controlled by a relais, so that there isn't always current flowing.
What is the "ground leg of the voltage divider"? Do you just mean ground?
And what do you think about this idea (schematics)?