I have also used this great little tool!

I am trying to use this setup but with high resistor value to avoid power losses. I understand that PIC ADCs requires a maximum impedance of about 1kohms for greater accuracy. However this would provide a large current draw.

My setup is as follow:



I use the resistor divisor to charge the capacitor, which is used to store the required amount of charges needed for a conversion. The drawback of this setup is that it lowers the number of samples per seconds, but for checking battery level it shouldn't be a big issue.

With the following setup I have a 23µA power drain and a time constant of 2.2 mS for the capacitor. Considering that 5 time constants are necessary to have 99% charge, let's say 10mS are needed to fully charge the capacitor. This means that I should space ADC sampling to no more than 100 times/s.

However, using the regular ADCIN gives me a first reading which is accurate, then either 0 or 1 for the next readings. I've also tried to manually configure the ADC but I have a hard time to understand how to configure it. Should I disable the dedicated RC oscillator and perform a manual "one-shot" sampling? The sampling time itself should not be limited as the 10nF capacitor provide the required charge to the ADC.