Thanks lefty, you've confirmed what I was coming to suspect.
The recommended 10k is the impedance in series with the input pin I assume, so the 2M resistor.
So, in theory if I could go to 10k / 7.5k then I'd end up with maximum 0.7mA drain @ 12V, per monitor line, or 2.1mA.
Let me just explain what I'm doing....
These board will run on battery power, from 7.2v to 12v input. Standard would be 5 x AA feeding, so 7.5V with 1500-2500mAh cells.
With usage of up to 250mA this gives me approximately 6-10 hours of expected life; my aim is for 8 hours on a single set.
I have the ability to use two sets of batteries to give flexibility for double the running time and/or swapping a set out without interrupting the running.
Now, the battery monitoring is intended to give a warning when a single battery set, or total power in, is getting low. This data will be contained in an RF 'heartbeat' via nRF, back to a base station to indicate if the batteries need changing. Being able to get the Vcc using this method also gives me a failsafe 'Code Red' warning if Vcc falls below 5V.
'Worst' case scenario is the device would be continuously running for 24 hours, so may need multiple battery swaps. Of course, the flexibility is also there to use a higher capacity SLA or LiPo type battery as a supply to mitigate this.
I will give the caps a try to see if that helps. The alternative is to decide whether the extra leakage will really affect my requirements. Even with 2 x 12V batteries then 2.1mA is less that 1% extra consumption, so would reduce a 6 hour running by less than 4 minutes.
Changing the 6 existing resistors on my boards would be easy enough. Adding the caps to the 10 boards I currently have would be more problematic, although could be incorporated into the next revision.
I'll breadboard a 1284 up and try the caps and different resistors to see if it fixes the problem.