Its not a battery.
Its a heat storage medium.
It has existed since the invention of fire.
We store excess solar daytime energy in hot water.
Thank you for standing up for basic technology literacy. The sand based heat storage system is the thermal analog of a capacitor, and it is definitely not a battery.
The fire you mentioned is a better analog to a battery...
However low temperature energy distribution and storage is still a useful technology. Waste heat can be re-used and thermal storage by mass is a good way to simplify heating systems. That's one good reason to build a large stone structure around fires used for heating. Things formerly known as fireplaces.