The battery capacity of the Galaxy S21 Ultra seems to be as good as confirmed, as suggested by yet another highly credible leak on the matter. Well, an early product certificate, to be more precise; one coming out of China, i.e. Chinese telecom authority 3C. The documentation concerns a battery carrying model number EB-BG998ABY. Which is a pretty unambiguous reference to the SM-998, previously identified as the Galaxy S21 Ultra.
According to this particular source, the Galaxy S21 Ultra will feature a non-removable battery with a rated capacity of 4,885mAh, amounting to a typical capacity in the ballpark of 5,000mAh. If all of that at least sounds vaguely familiar, that's because we already heard pretty much the same story in mid-September.
Equal battery capacity doesn't guarantee identical (or similar) battery life
It should also go without saying that a battery capacity identical to that of the Galaxy S20 Ultra hardly promises comparable screen-on time. Chip performance and user habits are both major factors that could tip the scales in either direction – and to any degree – once Samsung actually releases its next premium smartphone range.
As a reminder, the Galaxy S21 is just a tentative name for the series. It's still unclear how close Samsung actually is to greenlighting the moniker for marketing purposes. Recently, there's been no shortage of speculation about the Galaxy S30 brand, as well. Whatever the case may be, Samsung is expected to officially unveil its upcoming range of Android flagships early next year. February, to be more specific.