Zero or low-current voltage divider for switch identification
New answer

Your approach can work.  But, your 2nd schematic has a bug, I think.  The ADC will always see Vbe of the transistor, which is always 0.7V or so.

This variation shouldn't have this problem, because there's a resistor R39 between base and ADC.



Old answer, which wasn't an answer

The divider can be switched with a transistor to save the battery.  However, it has to be a high side switch.  If you switch at the ground, then the battery voltage will appear on the A/D pin, which could damage the input.



(Originally, the schematic was posted in this thread.)