Battery power back-uped circuit

[sayzer]

FVR is not at accurate, so that 4.25... I doubt you are safe.

Ioannis

Why is not not accurate?
I get 1.024V with 1x output.
And if the Vdd is 2,5V I still have 1.024V at my FVR output. I never encountered an accuracy issue.

But, if you have a high freq circuity on the same pcb, or even if your PWM module is running, then I agree, FVR can be disrupted.
Also, here is a simple circuit diagram for NPN-PCH charging. Assuming you are not charging the batt with high amps, LM317 would do the job. If not, change LM317 to a switching circuit to have higher efficiency and lower heat.