Despite the fact that before the announcement of the new flagship Samsung for about half a year or even more, the network already appears fairly reliable data about these devices.
In particular, it seems that we already know what batteries will get smartphones. For example, the alleged Galaxy S21 Ultra with catalog number SM-G998 will receive a battery with a nominal capacity of 4885 mAh, that is, Samsung will probably indicate it as 5000 mAh. Thus, there will be no changes with respect to the Galaxy S20 Ultra in this matter.
Galaxy S21+, in turn, will get a more capacious battery than its predecessor. Rated capacity will increase from 4370 to 4660 mAh, and the specified is likely to be 4800 vs. 4500 mAh of Galaxy S20+.
As for the younger model, the Galaxy S21 should get a battery with a rated capacity of 3880 mAh, that is, the real one will be specified as 4000 mAh.
Thus, a more capacious battery relative to its predecessor will get only the Galaxy S21+. At the same time, the autonomy may change in any direction for other models, as it depends on many other factors.