Thanks for al your answers, but none of them answers my question. To clear them out once more:
1. does N900 shutdown itself when battery goes low or does it just die when batt is empty?
2. if it does shutdown, what charging level does trigger this event? And where does it get read from?
3. might it be the power kernel changes this behaviour in any way? (not talking about power consumption, only shutting down when charge goes empty)