Power tool battery has been being widely used in industrial and civilian small electrical appliances. The advantages of it are mainly four points, that is, high energy density, high working voltage, long service life and wide working temperature range. The most obvious benefit of going with 18650 vs 21700 lithium rechargeable battery is that the extra density means there's more available energy in them to run your tools and gear longer. The cell of the 18650s has been grown to 1000 million and that of 21700s has grown to 200 thousand in 2020.