The first variant is the Galaxy S21, with the identifier EB-BG991ABY (SM-G991). Per the listing, it will pack a battery with 3,880mAh rated capacity.

Next up, the publication has spotted the EB-BG996ABY (SM-G996), which supposedly is the model number for the Galaxy S21 Plus. The 3C certification website suggests that it will feature a cell with 4,660mAh rated capacity.

Note that these are rated capacities and we can expect the typical values to be higher. 

To fill up the humongous battery quickly, Samsung is apparently planning to introduce 60W fast charging.

Additionally, the website also shows that Galaxy S21’s batteries will be manufactured by a Chinese company called Ningde Amperex Technology Limited.