The power module is a one piece integration that comes from one factory. It has batteries, smart charge electronics, output regulators, charge pads (not jacks, these contacts must be waterproof) and many will have solar cells. It has a diamond shaped hole in the center for the speaker and microphone module.
The main quality we must build into an electronic personal memory organizer, is that, it is guaranteed to not lose user memory. This can only be accomplished with adequate gauges and warnings (smart power hardware), made obvious by the display, about power charge conditions.
That is, until non-volatile memory is made in big enough quantities to be inexpensive. The system uses 5.5 volts maximum and 3.3 volts minimum. Maximum and minimum correspond to sleep and waking states - there is no true "off" in an electronic personal memory organizer. In case the user surpasses the amount of available energy, the unit "sleeps" until recharged.