There is a difference between placing multiple cells parallel or packs parallel. Multiple cells parallel You can safely place multiple cells parallel and only need 1 BMS cell module per parallel group. For instance: a 12V LiFePO4 pack consists of 4 cell groups in series. In case you have 8 cells, the pack is configured as 2P4S (groups of 2 cells parallel, then these parallel groups in series). In this case you only need 1 BMS for 4S (4 cell groups).
Multiple battery packs parallel When you have to connect multiple packs parallel, you need 1 complete BMS per pack. You can connect the signal relays on each OUT board in series. For instance: with 3 packs parallel, you can run the charging signal through from the first OUT boa rd Charge relay to the second Charge relay and through the third Charge relay. This signal can switch an enable/disable or power relay. When one or more BMS have a cell charge error, the signal path is broken. The same goes for the Load relays in series.