This source lists the test pads of the Pi Zero and their function as follows:
PP1 USB +5V Input
The official schematics (see top left corner) also list PP5 as GND.
Powering the Pi from AA batteries itself has been discussed before (such as buck/boost converters to adjust the voltage), e.g.:
- http://raspberrypi.stackexchange.com/questions/29902/powering-the-pi-with-2-aa-batteriesPowering the Pi with 2 AA batteries
Without proper voltage regulation connecting the batteries might pose some issues during discharge of the batteries - voltage is too high with fresh batteries, too low on empty batteries.