I am planning to use this in my project. The AVR microcontroller is asleep most of the time (less than 500 µA), and the current draw raises every minute up to 100 mA, but it lasts 500 ms maximum. So I think connecting the charger directly is not a problem.
In the original LDO circuit there are two Schottky diodes connected. I was told that the first one is to prevent reverse-voltage and the second to protect the LDO when Vout > Vin. I was also told that the first diode's voltage drop will prevent me from using the full capacity of the battery...
So I guess the best way is to remove the first diode. But is this circuit going to work at all?
The AVR battery voltage measurment is a voltage divider controlled by a MOSFET. The voltage divider ratio is 1:2, so the input voltage is always lower than the AVR's VCC.