In the parallel connection of lithium batteries, it is critical to ensure the consistency of battery parameters, including capacity, open-circuit voltage, and internal resistance. Only if these parameters are close can the batteries be paralleled, and for safety reasons, additional protection plates are required. In the case of multiple cells in parallel, if one of the cells has a lower capacity while the other parameters are the same, this poses some potential problems.

During the charging process, if the batteries connected in parallel are not equipped with a protection board, a charger with a limited voltage of 4.2V must be used to prevent the lithium battery from overcharging and causing explosion. Even if a protection plate is installed, the battery with low capacity will be fully charged first, and long-term overcharge will lead to an increase in the internal electrolyte and the occurrence of side reactions, which will lead to battery leakage. Batteries with low capacity can also be over-discharged during discharge, which not only reduces battery life, but also poses a risk of leakage. Therefore, batteries that have been in a state of overcharge and overdischarge for a long time have great safety risks, and may even cause explosions or fires. Considering that your battery comes from the power bank disassembly, the parameters may be inconsistent, and you are not sure whether a protective board is installed, it is strongly recommended not to assemble and use it by yourself, so as not to cause potential safety hazards.