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Below you find my three main sources. As you can see in the title I choose to built the powerwall with well known and widely available 18650s. 18650 stands for the size of this popular battery. 18mm diameter, 65mm long. It's capacity is somewhere between 2000 and 3500mah.
Good capacity, easy to open.
High capacity, high current, a bit harder to seperate the cells.
Low capacity, very high current. Relative easy to open.