Battery monitor/sensing ratio calculation

[FlyingSaucrDude]

Apologies for raising a long-dormant thread from the dead, but I was hoping to verify my understanding of the discussion that went on this thread.

From reading the thread above, I get the sense that the attached circuit should work if I want to measure the battery voltage only when I set the DIO pin to HIGH, and draw minimal current whenever I set the DIO pin to LOW.

Assuming that's correct, I have a couple questions:

• How are R1 and R2 chosen? Are they necessary for this application? This was asked above, but I didn't quite understand the answer.
• Is a capacitor in parallel with R4 necessary? I get that adding it would allow me to use bigger values for R3 and R4 (and thus use less current while I'm measuring). I also get that it would require me to wait a couple milliseconds (depending on the RC constant, which depends on the values of R4 and the capacitor). But is there any other benefit from adding it?
• Is there no off-the-shelf IC I can buy that combines all these components? I'm mildly surprised that "low-current voltage monitor in a single IC" isn't a thing that exists, but I guess maybe this is specialized enough that it doesn't make sense.

Thanks in advance for the help!

[Felix]

FlyingSaucrDude,
Thanks for the post but it was not really relevant to the thread you posted in, it's just a general vbat monitor question, so it's now a new thread.

Not sure what "this application" you refer to, the web photo you attached ? That's an overly complicated way to sample battery voltage.
If you can afford a sub microamp constant drain, then just use a [Vbat]->[1Mohm]<-ADC->[1Mohm+0.1uF]->GND voltage divider. Otherwise you can use a GPIO to toggle a single PFET that feeds into a divider, enable it only when you sample - in this case the 2 resistors can be much lower value for fast response. The ratio of the 2 resistors give you the Vbat divider, so 1:1 yields 50% of Vbat going to the ADC pin, this is when Vbat > VCC of the MCU. Otherwise if Vbat feeds directly into the MCU then you can use bandgap to sample the battery with no external components (not most accurate but with a little calibration its very accurate).
Many many voltage monitor ICs exist, you only need to search.