What does a slow cranking speed with excessive current draw typically indicate?

A slow cranking speed combined with excessive current draw is a symptom often associated with batteries that are sulphated. Sulphation occurs when lead sulfate crystals build up on the battery plates, which can significantly reduce the battery’s ability to hold a charge and deliver the necessary current to start the engine. When starting an engine, a sulphated battery struggles to provide the needed voltage and current, leading to slow cranking.

In the other scenarios: a fully charged battery would generally show normal cranking speed and current draw; a functioning alternator would ensure the battery is being adequately charged while operating; and low viscosity engine oil could increase cranking speed, as it allows engine components to move more freely. Therefore, the situation described is clearly indicative of sulphation in the batteries, affecting their performance.