Thanks for all the responses. It probably would have been a good idea to state in the first message that I’m a professional, electrical engineer, installer and a contractor with 11 years of experience with solar systems. I am looking for a software solution to activate the battery’s own heating elements. DIY solutions are a different topic.
@OGPS 100-150mm urethane insulation is all around the battery box which is pretty good. A typical Finnish house has 250mm insulation wool (or approx 150mm of advanced polyurethane insulation) in the floor and walls and 500mm insulation wool on the attic/roof.
@ChiefSolar Yes, the batteries have that label and have internal heaters. The batteries are new.
The solution might be really simple, but problem is that Dyness provides no documentation what so ever. I haven’t accessed the battery settings. The manual only describes simple DIP switch configuration and that’s it.
I now found online that there is a “external WiFi stick” available. Maybe that would give access to the device.. Weird that none of this is mentioned in the manual.