Problems that will occur when inconsistent batteries are used in series.
Capacity loss. When discharging, when the lowest cell voltage reaches the discharge cut-off voltage, the whole battery pack stops discharging; When charging, stop charging when the highest battery voltage reaches the charging cut-off voltage. When charging, the battery with small capacity must be fully charged first to reach the charging cut-off condition, and the system will not continue to charge. The life of the battery pack is determined by the battery with the shortest life.
The greater the internal resistance, the greater the internal resistance, and the same current flows, the more heat the battery with large internal resistance generates. If the battery temperature is too high, the degradation speed will be accelerated and the internal resistance will be further increased. Internal resistance and temperature rise form a pair of negative feedback, which accelerates the deterioration of high internal resistance batteries.