>So the other method of using the A/D would require a voltage divider,

Maybe, but not necessarily.

>albiet you could go with higher impeadance decreasing the current draw,
>and followed by a opamp configured as a voltage follower, simply to
>keep the input impeadance low on the input.

The starting question here is are you going to be doing any A/D stuff 
anyway? If so, what are you doing for a stable reference?

The neat trick with monitoring battery voltage is to use a stable reference 
for your normal measurements, and then when you want to measure the battery 
(actually this will measure the PIC supply voltage) is to switch the PIC 
into using the supply as the reference, and measure the reference voltage 
input using the ADC. This gives you a reverse scale though, i.e. a bigger 
number from the ADC means the supply is lower, but if you are running the 
chip off an Li-Ion or other <5V battery, then this gives a direct measure of 
the battery voltage assuming the stable reference is less than the lowest 
battery voltage, and can maintain regulation at that battery voltage.

There some reference chips around with blindingly low current requirements, 
but I do not know off hand what the required source impedance for the 
reference supply on a PIC is. It may need to be the same as a normal 
analogue input, which may mean using a higher current device. But as others 
have suggested, using a spare digital pin to turn the reference off and on 
may mean this is of minimal consequence. 

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