BATGUARD is a module that automatically disconnects a load when the battery voltage drops under a given threshold. It prevents the vehicle battery to discharge too much when not loading.
May seem counterintuitive to use a LDO. But the DC/DC TRACO converter I used adds a no load overhead of about 15mA. I had some very low dropout regulators (LP2985) in my spare components, reducing the consumed power to 23.4mW (due to the low current drained by the MCU). There may be DC/DC dedicated to low power applications. To be investigated.
Cool name, I totally thought you made bats (like animal) ultrasound sensor :)