Not always, but the savings are best when you have solar panels installed.

Your battery takes advantage of both solar and the Economy 7* cheap overnight tariff. For the battery only case, the more electricity you use, the more cost effective it is, so it is particularly suitable for large domestic or commercial situations.

Update 2022: Due to the current price increases in the cost of electricity a standalone battery can now make good financial sense, as well as providing the option of battery backup in a power cut.