Sensing 3V-4.5V battery w/o booster

[rlogiacco]

On behalf of a user:

I'm looking at your library and I wonder if, for a 3.3V powered Arduino board (actually, a moteino with no booster) is or not a good idea to switch to the internal CPU reference of 1.1V using analogReference(INTERNAL) ...
Looking at your example code it seems that you are not setting the reference at all... Am I missing something?

[rlogiacco]

No, you actually need to use a voltage divider in order to scale down the battery voltage within the limit of the board: a voltage divider with a ratio of 2 will be good.

There is no need to set the analog reference to 1.1V unless you have other code in your firmware which manipulates it, anyway what you are looking for is the DEFAULT reference which, in your case, is 3.3V: the voltage you want to measure is much greater than 1.1V.