At the Amazon Bluetti pages I found this image of the B300S insides:
As you can see, there are four main packs of four stacks of fifteen cells (blue). I calculated that the arrangement is 15P16S. Here are my calculations:
Each LiFePo4 cell is rated at 3.2 V and 4 Ah.
Each stack of 15 cells in parallel make 15 x 4 = 60 Ah (the expansion cable is rated at 150A so the 60 Ah can be discharged at a faster rate).
Each pack of 16 stacks in series make 16 x 3.2 = 51.2V which is posted on the B300S label.
The total energy of the B300S is 51.2 V x 60 Ah = 3072 Wh
The B300 should be similar since it has the same Wh rating. Now we know what is inside without needed to open it. Although the Amazon image shows the cells, the BMS circuitry on top, and some of the DC sockets, it does not show the four inner expansion ports sockets or cabling.
Extra: If anyone has a damaged B230 or B300 and needs to dispose or part it, please write me at rayramirez@prtc. I am interested in reusing the cells for a automobile battery replacement.