Battery testing sensors, and systems and methods for testing batteries, are disclosed. Each battery sensor has a microcontroller programmed to analyze the frequencies of noise or other undesirable signals (“background noise”) present at a battery to be tested, and to determine the duty cycle of a desired pulse width modulation (PWM) signal to be applied to the battery in view of the background noise. Duty cycles of desired PWM signals are selected such that, when applied to the battery, they will at least approximate an AC signal having a frequency that has been determined to provide optimal test results in view of the background noise. The microcontroller analyzes the battery's response from application of the PWM signal thereto. Consequently, measurement errors from background noise present at the battery are minimized. Based on the response, attributes of the battery, such as internal admittance, voltage, current, and temperature, are determined.