Solar LiPo battery charger: revision and improvement of the reverse voltage protection circuit for the battery
You've made a mess of the charger circuit: -



Your "switch" node doesn't have a schottky diode to ground and it appears that your boost capacitor is inappropriately connected.

It looks like your reverse battery protection will work but why over-complicate a reliable standard circuit such as this one: -



Is it because of the charger circuit might keep the MOSFET activated and drain the battery?