I have a Victron ESS system with MultiPlus-II inverters and a Cerbo GX, and I live in a country with unreliable grid power. Today the grid voltage has been 103-109V, and I noticed that the ESS system has also been outputting 103-109V. This is with batteries full and power coming from the batteries/panels and nothing being drawn from the grid. If I switch off the breaker that disconnects my system from the grid, the voltage immediately stabilizes to 120V (still coming from the batteries).
I was expecting the Victron system to regulate voltage to 120V, especially when drawing from the batteries and not the grid. But it looks like as long as the grid is physically connected, the Victron system outputs the same low voltage that's present on the grid. Is this expected behavior? If so, is there anything we can configure to avoid this situation (maybe setting a limit to auto-disconnect the grid at 110V or so)?