[VladTheImplier]

There are great guides on how to lower power consumption by turning HDMI off, under clocking, even going as far as turning off the status LEDs. Killing off many of the autostarting services in raspbian or not using raspbian in the first place can also help quite a bit due to peak current draw during boot time. If you don't need networking you can easily get down to almost 10s boot time by disabling networking daemons and dependencies.

Made a project in optics with the pi zero w, camera v2, a touchscreen over GPIO, 4 bright LEDs and a 5V regulator. As a power source it uses a 9€ 1200mha LithiumIon Battery in 9V battery form. Lives on for 3 hours under full load.

Also using normal 9V batteries I killed them in 5mins - something something internal resistance of non LithiumIon batteries not coping with high current draw.