You may be forgetting that batteries don’t have to be electrochemical; one technology from before WWll pumps water up a hill when you have excess supply, like lots of sunshine or wind, and when you haven’t the water runs back down generating electricity. The technology is well understood, costs little to run, and has a decades-long lifetime.
True to an extent. Pumps are well understood. Water's well understood. We know water naturally doesn't want to be up a hill. So you'd have to find suitable hills, dig out large reservoirs, dig tunnels down into the hill, dig out turbine halls and dig out another reservoir to catch the water. So basically more Dinorwigs. But the UK has a lack of suitable hills, and people would object to digging them out. Not to mention the cost and cost of dealing with Nx12mt or more surplus rock from excavations. One possibility might be landfill for the Swansea tidal lagoon to create more waterfront property.
Then there's the cost. Not only the construction, but buying 'renewable' energy at £100/kWh+, adding the storage costs and then trying to sell that electricity when the market rate is £35/kWh or less.
Like much in the renewables scam, everything is great, if you just ignore the economics. And for the UK, there's still the challenge of 'decarbonising' heating as well as transport. So not just forcing everyone into EVs, but forcing them to use electricity for heating and cooking.. Which massively increases demand, and means gizmos like Powerwalls would run flat even faster.