The range for input is 0-3V. You need a voltage divisor to estimate the total voltage.

p.e.: trying to mesure 9V, use two resistors, 1 of R value and the other 2R, connect the battery to the exterme of the two resistor in serie, use high value to avoid dischard the battery quick. The signal to the input between the two resistor and after you have to apply the formula (value*3)/1023.