For my engineering project, I'm thinking about powering the arduino through 3 AA batteries. Is it possible to power the Arduino using 4.5V?

 

Which arduino do you have? Will you use the USB interface during battery operation?

 

Most Arduinos require a minimum of 6V input (7V recommended) that's regulated to the logic level of 5V. A few Arduinos, like the Pro Mini, have 3.3V versions and require a minimum of input voltage of 3.35V.

 

If you read the data sheet for the uno it can use both 3.3 or 5 volts and it has blocking diodes to keep you from back feeding the usb and the regulator.

You can pull the chip and use it at 4.5 volts leave it in the uno board and use a wall wart you need 7 to 12 volts but it will work with 6 to 20 volts but they want you to use 7 to 12volts

If I wanted to use it at 4.5 I would buy a ATMEGA328-PU and program the bootloader on it and use it in my project.

 

If you read the data sheet for the uno it can use both 3.3 or 5 volts and it has blocking diodes to keep you from back feeding the usb and the regulator.

Where are you seeing this? I'm looking at the specs and see 6V minimum input voltage.