The disclosed battery monitoring systems and methods may minimize measurement errors due to noise and/or other disruptions. The sensor may generate a pulse width modulated signal that when applied to the battery forms an AC test signal having a defined waveform, frequency, amplitude, and/or duration. The sensor may measure the battery's response to the test signal. The resultant response signal may be measured to determine the health of the battery, including its internal admittance. The sensor may determine an optimum frequency to test the battery by scanning a frequency range and measuring the amount of noise present.