As I teach my students think of Volts = number of lanes in a highway, Amperage = the speed of vehicles on the highway, and Watts = the number of vehicles on the highway for a given time.

Another way to view is Volts = size of the fire hose, Amperage = the amount of water coming through the hose, and Watts = the power of the water moving.

So my measuring the total actual draw (load) on the battery in use, you then are measuring its amp use. Multiply that by a time factor and you have wattage. The volts is the conduit or steady stream in a sense.