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Batteries based on lithium ion hold many advantages over other battery chemistries, such as high power density and a flat discharge curve, and are the dominant choice in everything from smartphones to electric vehicles.
Depending on the particular Li-ion chemistry used, the voltage of a single cell is between 3.3 V (LiFePO4) and 3.7 V (LiCoO2). A battery pack consists of several cells connected in series—a pack with two cells is a “2S” battery and outputs 7.4 V; a 3S battery outputs 11.1 V; and so on.
In consumer applications, a 1S battery supplies enough power for a personal electronics device such as a fitness band or smartwatch. Industrial and heavier-use consumer applications require larger sizes: 3S or 4S for small power tools or drones; 5S for professional power tools; 7S for vacuums; 10S for garden tools or larger power tools such as saws; and even 20S for heavy-duty applications like forklifts.