To be a bit more precise, at 1000 watt load the Sunny Island 6048 is about 95% efficient, so add 50 watts.
It appears the 25W idle current is included in the graph below, so 1050 watts.
At 6000W load around 92% efficient. 6000 / 0.92 = 6522 watts from battery.
View attachment 29277
I'm able to curve-fit the efficiency fairly well with the following:
PowerLost = 25W + (0.4% x PowerDelivered)^2
The "squared" would come from IR^2 losses, dissipation in MOSFET and transformer goes as square of current.
I only took a few numbers from the above graph. This equation provided a reasonable fit but not TOO good, as in the following link:
The “conversion penalty” at 48v will be quite a bit lower than 15%. For a Victron unit, I can tell you it will be 8% or less. Victrons are top shelf and have demonstrated ~90% efficiency. Anyone want to test their mpp 48 volt all in one unit?
diysolarforum.com
Sunny Island shuts down to protect battery from over-discharge, default 80% DoD (at least for lead-acid). Each inverter has two relays which can be programmed with various status, including two states of charge. 70% DoD is default for load-shed, disconnecting non-critical loads so inverter can keep running until sun comes up.
Some charge controllers (e.g. Midnight Classic) have programmable relays. I think state of charge is one option, so could control load-shed or inverter shutdown.