thats exactly what a 2S is, 2 in series. 3S is 3 in series. normally you see two connectors on the battery, a 2 pin - your main power output, and a 3 to 6 pin depending on the number of cells. the multi pin connector is for balance charging and connnects to the charger so it can see the voltage of each individual cell and make sure they are all exactly the same.
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