The big taboo of using lithium battery in series is the serious imbalance of battery self discharge. As long as everyone is in the same unbalanced state, it doesn't matter. The problem is that this state is unstable. The self discharge of a good battery is very small, and that of a bad battery is very large. The self discharge of a bad battery is not very small, which is generally from a good state to a bad state. This process is unstable. Therefore, it is necessary to screen out the batteries with large self discharge capacity and only reserve the batteries with small self discharge capacity.

On the basis of small self discharge, series connection with similar capacity is selected. Even if the capacity is not similar, the battery life will not be affected, but the usable capacity of the whole battery will be affected. For example, if 15 capacities are 20Ah and only one is 18ah, the total capacity of this battery can only be 18ah. In the end, the battery runs out of power. The protection board needs to be protected. The voltage of the whole battery is still high (because the voltage of the other 15 batteries is normal and still has power). Therefore, the discharge protection voltage of the whole battery can see whether the capacity of the whole battery is consistent (provided that each cell is fully charged when the whole battery is fully charged). In a word, the unbalanced capacity does not affect the battery life, but only the capacity of the whole group, so try to select the assembly with similar capacity.

The good ohmic contact resistance between electrodes must be achieved when assembling the battery. The smaller the contact resistance between the wire and the electrode, the better. Otherwise, the larger the contact resistance, the electrode will heat up. This heat will pass along the electrode to the inner part of the cell and affect the battery life. Of course, the performance of large assembly resistance is that the voltage drop of battery pack is large under the same discharge current. (part of the voltage drop is the internal resistance of the core, part of the assembled contact resistance and wire resistance)