The problem there is numbers at least according to the manufacturers sell products, because they are "bigger".
And that is unfortunately I suspect true.
Hence the other focus on the dual cameras, because two are better than one seemingly.
In this case I think that was actually a downgrade in some situations.
Remains to be seen how much is hardware, and how much is software.
The latter can potentially be fixed, not the former without a new release.
Snapdragon 835 seemingly 20%-ish more efficient than the 821.
Seeing some comments online suggesting a similar battery life or more even with a marginally smaller battery capacity.
As for comparison with another, typical usage is going to be inconsistent so difficult to compare.
Though light to moderate usage is said to last two days.