Increasing Battery Voltage

I'm hoping someone can explain what is going on here.

I don't currently have a TOU tariff so on occasions the battery will run out overnight, but when it does the voltage seems to constantly increase despite no reported power going into it.

Last night the battery ran out at 21:20 (at 6% despirte the default 4% cutoff) and after 30-60 mins the voltage was around 51.6-51.7, but the voltage continuously increases from there despite the battery power reporting as 0W, at midnight it is 51.86

This continues into this morning, at 1am with a voltage of 51.9 it increases the battery percent to 7 (despite no reported power being put in) and at 4:40 having hit 52.06V, it decides it can power the house, it does so for ₅₀ mins until empty and then it goes back to the grid.

This cycle would continue but once the sun makes an appearance that takes over and the battery starts charging from that.

This has happened since the system was installed and while it's not really causing me any problems I'm just a bit confused! System is Hybrid 3.6 Gen2 with 9.5kWh battery.

I think you are just seeing the battery recovering a bit. When the battery is discharging into a load, the voltage will drop a bit, and when the load is removed the voltage will rise a bit - and as you have observed, it may continue to rise a small amount as well.

7 hours feels like a very long recovery!