Does the battery have BMS on board? or does it have any over/under voltage protection, over charge/over discharge current protection, battery temperature protection & cell balancing, and if not are there any related products that have these functionalities?
No, there is nothing but battery cells in the battery pack. No integrated electronics or protection circuitry.
In our BlueROV2 vehicle, we use an external power monitoring module to monitor the voltage and current, and we sell a smart charger that will charge and balance the cells correctly.