What I am really interested is knowing how these "Chinese Batteries/BMS" behave with the Sunny Island in an AC Coupling setup with closed loop communication. Especially when these batteries are not in the SMA Batteries "approved" list.See page 16 for BYD battery quantity to support various number of Sunny Island. That would be for AC coupled systems, able to supply power and accept charging, while doing frequency-watts management.
You could try to scale specs of the BYD battery to those of a different brand. But voltage setpoints requested by BMS would be important to leave headroom to absorb the kW for a few seconds.
BMS should be communicating with the Sunny Island at all times or the SI will switch to standby mode after a minute (or so) of missing communications with the BMS. So when the battery is full the BMS cannot go into sleep mode or stop communicating with the Sunny Island.
Also interested in knowing what the Sunny Island will do if there is an alarm (i.e overvoltage alarm). Will it stop charging and stay on or will it go into standby mode and therefore house will shut off. Stuff like that is what I am trying to find out before dumping a few thousands on two LiFePo4 batteries for my two SI6048US.