Vehicle battery monitoring method and assembly

A monitoring method, comprising:

• within a vehicle, providing a first electrical system with an auxiliary battery, and a second electrical system with a primary battery;
• electrically coupling the first electrical system to the second electrical system;
• electrically loading the auxiliary battery and the primary battery;
• and
• comparing an electrical parameter of the auxiliary battery to a threshold value to assess a condition of the auxiliary battery,
• wherein the vehicle is a stop-start vehicle, wherein electrically loading the auxiliary battery and the primary battery includes cranking an engine of the vehicle at a start of a vehicle drive cycle, and further comprising, later in the vehicle drive cycle, stopping the engine and then warm cranking the engine using a starter generator powered by the primary battery.