[Serum]

if you put them in series, it goes like this;

one red and black wire are unused and are considered a connection to make a 4S pack, a 2S pack uses 3 wires. one 0V/black, one 3.7 and one 7.4. between the 3.7 and 7.4 tab is a 3.7V again;

now if you put them in series for 4S, you need a total of 5 wires. and each wire differs the 3.7V of the cell. the two most outer wires measure ~18.5V.