I need to build voltage divider to measure the battery voltage (7.3V) using max 3.3V ADC. As the device most of the time spends in the sleep mode (<1uA), the current drawn from the battery should be very low (best <70nA) so the resistance of the voltage divider has to be > 100MOhm.
I know that I need to buffer this voltage but I struggle to design the voltage follower working with such a high impedance source.
My question is: will JFET input opamp (as I know they have high input impedance) will be good for this application?
Maybe there is another method of lowering the voltage which will draw such a small current form the battery.