[Alexr]

Hybrid battery runs almost all accessories, so whatever you have on, it will deplete hybrid battery quickly. 12v standard battery really only carries out ECU boot-up.

If you see battery level at full, it means your not using EV mode enough.

Sorry to contradict you but this is completely wrong. The hybrid battery runs at 200+ volts so is not used to power accessories. It drives the electric motors to drive the wheels, and it is used ( via a convertor) to provide 12v charge to to the 12v battery which then runs the accessories, and the power usage of the accessories is very low compared to the hybrid battery power, so it wont deplete quickly from them. And (as has been said) battery level does not indicate your usage of EV, in fact most people recommend not using EV (as in the EV button) and let the car run in EV when it chooses to.
But the 12v battery does do the boot up, so a flat 12v battery is a dead car, even if the hybrid battery is well charged. So even a small charge applied to the 12v battery at startup can get you going ( far less than a conventional starter motor uses).