At $5500 (is that including GST?) for a 7kWh model, with a ten year life, and allowing for interest, that comes in at about 28 cents per kWh, and that's before the cost of the solar panels and the inverter (not included with the battery), and installation, is included. It's also based on the questionable (i.e. certainly false) assumption that they can be recharged from solar everyday. The reality is that they won't be, and the cost per kWh will be accordingly higher.
The limit of 2kW continuous and 3.3kW peak should also be noted. It isn't clear how long one can draw 3.3kW for, but 2kW is less than is required to run an ordinary domestic kettle. A typical household might have trouble using the entire capacity, pushing up the effective cost per kWh.
The good thing about these is that they may finally force a change to the way electricity is charged for, with much greater emphasis placed on the cost of making it available versus the cost of supplying it when it's required. People who treat the grid as a backup will then pay something closer to the true cost of using it that way.
Either way, I'll have to look at that the economics of charging these on overnight off-peak power (generated by coal fired power stations) for use during the evening peak when the much more expensive power would otherwise be generated using less polluting natural gas, or even hydro.