>I've done it in the past, with a 9V battery supply, by switching the
>battery supply with a transistor into a 2:1 divider (10K+10K).
>The neat trick is to use a capacitor to level-shift the switching
>signal. You only need to check bat level occasionally, so drain is
>minimal, accuracy is good as you can use a lower resistance divider,
>and it takes no power when not active. You can often also dual-use a
>pin for the switch signal.
>
>PNP transistor - E to +9V, C to divider (10K/10K with centre to ADC
>input).
>100K from E to B, 100K + 10n cap in series with B to I/O pin. Take I/O
>pin low to enable voltage for a few mS - long enough for ADC
>conversion.

Now that is a sneaky way of doing it. I like it.

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