I just had my second 6500EX48 do this very thing after 1.5 yrs of operation. I was not home the first time that it happened (2P2), SS tried to blame improper startup procedure on the first one but sent a replacement anyway. This one happened on Sunday afternoon about 2:45PM. SOC 100% for a couple hours. Almost no load on the system. 2P1 died. I went to the basement to find the main battery input breaker tripped as well as battery 11 and 12 in the daisy chain tripped. Since this was very similar to the first time, I went straight to the battery inputs and they were shorted - zero ohms. Most certainly did not happen during start up. Full disclosure - I am was running EMP shield protection on the PV in, and added them to the batteries and on the house breaker box after the the first failure. I sent the PV in shields back and had them tested. They came back fine. Waiting to see what SS does with this failure...