Solax batteries not fully charging

Hi, apologies, new here and not really that technical but i’m after some help please. I have a Solax inverter and 3 x Solax Triple Power batteries (17.4kWh). I also have a 6kW solar panel system. The batteries are in the loft. Recently, the weather has been quite cold (around 8 degrees C in the loft) but there has been some good sun. The panels have been generating around 3.8kW for a good few hours during the day. The batteries were at around 40% but the inverter split the 3.8kW from the panels in a strange way. 400W went to the house to run whatever was on but only 1.8kW went to the batteries. The rest of the power went to the grid! Why would this happen when the batteries weren’t full? During the summer, the batteries took anything that was available so i’m thinking it may be a temperature thing? I’ve not changed any settings on the inverter so i’m really confused as to why this is happening. Can anyone shed some light on this please. Thanks.

I’ve not got batteries, but I do know that most BMSs have temperature monitoring, and will either throttle or cut-off charging below a certain temperature. Check the manual to see what temperature that is.

My house temperature monitoring is telling me the loft has been seeing near-0 in the last few days, so it’s probably the temperature.