SOH refers to the capacity, health and performance of the battery. Simply put, it is the ratio of performance parameters to nominal parameters after the battery is used for a period of time. The new factory battery is 100%, and the completely scrapped battery is 0%. It is the ratio of the discharge capacity of the battery to its corresponding nominal capacity at a certain rate from Wally state to cut-off voltage, which is simply understood as the limit capacity of the battery. The internal resistance of battery has a certain relationship with SOH. The lower the SOH, the greater the internal resistance of lithium-ion batteries. By detecting voltage, current, temperature and other data, the internal resistance of the battery is calculated indirectly, and then SOH is calculated according to the relationship between SOH and battery internal resistance.