I was wondering how to use battery life as a factor in the code. For example, if I wanted to make a buzzing sound when the battery life got below a certain percentage. P.S. I am using the LilyPad Arduino.
A lot of microcontroller ICs have something called brown-out detection, which detects when the supply voltage gets below a certain amount. I would recommend looking through the datasheet for whatever board you have and see if it can be accessed. Perhaps there is an internal status register for the chip that can be read.
What do you mean by "battery life"? How will you measure how old the battery is? How will you know when it will die?
Other than those two minor problems, the rest of what you want to do is easy.
Don't use brownout detection. That is more like the emergency shutdown when the battery is too low to continue running anything.
If you have some means of estimating the battery percentage then making a buzzer go on is trivially easy. But the first part of that "if" is not easy at all and you now have a problem with your buzzer draining the remaining battery very quickly.
Thank you for your responses! I am new to the LilyPad Arduino and coding in Arduino C. I am trying to figure out how to estimate the battery percentage and send a warning via buzzer based on that. Unfortunately, I do not know how to get the computer to estimate the battery percentage and use it in the code. If someone could help me with that I would greatly appreciate it.
If you are talking about the battery supplying the arduino, you would try to detect when the voltage drops below a certain threshold. You can read the voltage in the arduino with "the secret voltmeter".
What kind of battery? The Sparkfun LiPo fuel gauge works for LiPo batteries (obviously.)