hehe....they are called deep-cycle marine batteries.
And they weight about 150Kg each.
And they are not cheap. 8O

Plus we are in sunny Hawkes Bay 8)

We dont use this on all of our infrastructure any more but it works very well.

The key is to use very low loss (read expensive) charge regulators and efficient power supplies.

The set-up we used went fine for a good 8 months before we pulled it down and rebuilt from scratch.