Low Current Battery Monitor Detail Question
The first circuit is fine (provided the P-channel MOSFET gate-source breakdown is sufficiently high to be safe with the battery voltage across it). It's equivalent to the original circuit with lower power drain when on. Full marks. 

The second circuit will not work at all, as neither transistor will turn on fully. Even if if Q1 turned on fully, Q2 would drop a volt or two and your output voltage would be inaccurate. 

You need to have the gate of an N-channel transistor more positive than the source by a few volts for it to turn on fully. In your second circuit, both gates would have to be higher than the battery voltage by a few volts to fully turn on.