When connecting lithium batteries in parallel, the key is to ensure the consistency of battery parameters, including capacity, open-circuit voltage, and internal resistance. Batteries can only be connected in parallel if these parameters are similar, and for safety, a protection board is required. In the case of multiple batteries connected in parallel, if one battery has a lower capacity while the others have the same parameters, this can lead to some potential problems.
During charging, if the parallel-connected batteries do not have a protection board, a charger with a voltage limit of 4.2V must be used to prevent overcharging and potential explosion of the lithium battery. Even with a protection board, the lower-capacity battery will fully charge first, and prolonged overcharging can lead to increased electrolyte levels and side reactions, potentially causing leakage. During discharge, the lower-capacity battery may also over-discharge, reducing battery life and increasing the risk of leakage. Therefore, batteries subjected to prolonged overcharging and over-discharging pose significant safety hazards and could even explode or catch fire. Considering your battery was salvaged from a power bank, its parameters may differ, and it's uncertain whether a protection board was installed. It is strongly advised against attempting to assemble and use it yourself to avoid potential safety risks.
