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That's something else I noticed. My US3000C loses ~12% in 10h (from 8pm to 6am) in SOL mode while the loads are supposed to be powered exclusively by the grid.

Hi, first message here. I've had the SPF5000ES with 8x465w panels and without batteries since april 2021, running in SUB mode most of the time and mixing solar + grid when solar wasn't able to power the loads. Last weekend I've added 1xUS3000C and tried SUB mode expecting the loads to be powered exclusively with solar and with solar + grid at the same time when solar wasn't sufficient as I was used to (and described on manual's page 16). That didn't happen. The solar generation stopped (battery were at 100%) and the grid started to power all the loads exclusively. So I've changed the mode to SOL and I'm happy with it. Solar as first option, solar + batteries when needed (almost never), and when PV voltage drops under 120v OR battery drops under 50% (configured on P12), it uses the grid. My battery is configured to charge only with solar and I retain 50% of its capacity as backup.