That's not quite right. The battery voltage is 7.4V end of story. That will never change. Obviously the voltage lowers the more you use it, but the calcs will still be the same for both of those scenarios.
With the case of a 1.8 Ohm load, like an Aspire head; This Will deplete faster than a 3 Ohm carto set at 4.9V or a 2 Ohm carto set at 4V. Why? Because 4V is the lowest the BB can go. At it's lowest, the BB will be delivering more than 8 Watts to a 1.8 Ohm Aspire head. THAT is why people are getting less battery life. Also, it makes the comparisons not like for like.![]()
I see your point in that the BB delivers 7.4vdc to the step down and is constant regardless of output voltage setting. But since the BB's lowest setting is 4vdc, the end user can achieve longer battery life by selecting a wattage below what the BB outputs at 4vdc and 1.8ohms by using a higher ohm carto and selecting a lower wattage output, this has been my point all along.
You are defiantly correct that at the same wattage through the BB circuits, the battery life will be the same if the wattage were the same regardless of ohms.
Dan

