set audio alarm for when charger is disconnected
This can be done by using the pmset -g batt command. The first line of output from this command indicates your power source, e.g.:

Now drawing from 'AC Power'

Or

Now drawing from 'Battery Power'

A possible use for this might be to change various commands together in a batch file, e.g.:

pmset -g batt | head -n 1 | grep "Battery"


In the above example, you'll only get output when you're running on battery power. So, a reasonable approach might be to use a bash script running via launchd or as a hidden Login Item in your profile. Something like this would work a charm:

#!/bin/bash
while true; do
  if $(pmset -g batt | head -n 1 | grep -q "Battery"); then
      say "Running on battery";
      sleep 5;
  fi
sleep 5;
done