Battery Status notifier I am new to Arduino, and I am aware that unlike Raspberry Pi you do not have a full blown OS with many custom applications running concurrently. 
I plan to start an Arduino project with an Arduino NANO that will need to be portable, and include batteries. How may I get the battery status information without disrupting the rest of the functionality?
Use analogRead to measure the voltage on the battery. You might have to use the internal 1.1V reference to get a good reading. 

Don't write any blocking code and the processes won't interfere with each other. That means no long for or while loops waiting for something to complete and absolutely no delay.