Under normal circumstances batteries do _not_ heat up during charge/discharge, both the BMS and their internal electrical design (most of the cells are connecte

Under normal circumstances batteries do _not_ heat up during charge/discharge, both the BMS and their internal electrical design (most of the cells are connected in parallel) are intended to prevent that. And you connect the batteries in parallel too. The current in individual cells is not significant enough to cause any visible temperature changes even when the whole pack makes hundreds of amps @48v.