If they're asking $250 for a 15 cell battery, they got plenty of margin for protection circuitry. You have to watch every cell to make sure it doesn't go past the minimum., or it's at risk of being damaged.
All I see is 2 or 4 pins going to the tool on these batteries. There's an internal BMS in there. Otherwise you need an extra 16 wires to monitor the cell voltages.