Thank you Hamwich. In that case, I can't see any point to them.
The point to having batteries is that without a FiT contract in place you don't earn any money from solar power you export to the grid. ….
Except you can earn money that you post to the grid… of course it’s a different rate vs what you consume, and you need a smart meter… eg https://octopus.energy/blog/outgoing/ is currently 7.5p per kWh