Since I'm the one who asked you to try this in order to know if the noise in your circuit was due to the negative voltage charge pump or not...
3 brand new AAs in series will give you close to 5V, if they are a bit used it will be more like 4-4.5V but this doesn't really matter.
When you wire several batteries in series, the resulting assembly has a "+" terminal and a "-" terminal.
If you wire the "battery -" to "ground" then the "battery +" will be at +5V relative to ground.
If you wire the "battery +" to "ground" then the batteries will be the other way around and thus the "battery -" will be at -5V relative to ground.
In both cases there is 5V between the "battery +" and the "battery -" terminals. Which means there is -5V between the "battery -" and "battery +" terminals if you turn it around.