Which of the following is a common sign of a failing battery?

A slow engine crank is indeed a common sign of a failing battery. When a battery is unable to hold a charge or is nearing the end of its life, it may not provide enough power to turn the starter motor efficiently. As a result, the engine may crank more slowly than usual when attempting to start the vehicle. This can happen due to several factors, such as sulfation buildup on the battery plates, internal short circuits, or simply old age of the battery.

In contrast, rapid engine acceleration does not typically relate to battery health; rather, it usually concerns other systems like fuel delivery or engine performance. Increased fuel efficiency is generally not a symptom of battery issues, as this is more related to fuel system efficiency and engine tuning. Clear windshield wipers pertain to the windshield wiper motor and its functioning, which is not directly impacted by battery health. Understanding these distinctions helps identify battery issues versus other potential vehicle problems.