I put a Bluetti powerbank (that was surplus to requirements as I don't use it in the van any more) in the shed at the bottom of the garden. A solar panel (also surplus...) on the south-facing roof, and Robert's yer mother's brother.
It looks after itself, and has never gone below about 75% charge. Obviously costs nowt to run (yes, I know, upfront costs etc) and gives me 230v outlets (4), 12v outlet, and a few 5v ones, which run led strip-lights overhead and two pir led strips on the front and rear outside walls.
Perfect for my needs.