Anecdata, I recently had to replace batteries in several smoke alarms. 3 were Duracells and 2 were Rayovacs. All Duracells were from 2016/2017, i.e. assuming they were installed right away they lasted around 5 years. Rayovacs were from 2010 and 2011, despite both brands being rated for 5 years. It is possible that old Rayovacs were installed around same time as new Duracells and both lasted around same time, still makes for an interesting datapoint.