Battery sensitivity of few circuits

On X axis is battery voltage from 0 to 15V. On Y axis is gain. All circuits are from ngspicesjs examples

Common emitter:

Emitter follower:

2-transistor bootstrap amplifier:

Some weird 2-transistor french amplifier:

High-gain 2-stage common emitter:

Mosfet 10x amplifier:

Opamp piezo buffer:

Green ringer octaver pedal: