The quote is from this sample : Measuring and Reporting Battery Level
Use a 1MΩ (R1) and 470KΩ (R2) resistor in series, connected to the positive terminal on the battery and ground and then connected the tap point to the A0 input on the CPU.
The tap point could be bypassed with a 0.1 uF capacitor to keep the noise level low, at this otherwise high impedance point.