We didn't get batteries but are awaiting the deal to be part of the grid before we buy as the payback was 25 years.
It's quite a complex matter to calculate a payback for batteries, as it depends on the baseload of your house, the normal amount of excess your panels deliver, the battery capacity, how much your export is worth, your projection of future electricity prices, and of course the future time value of the money you're going to spend.
We didn't bother to figure it out exactly, we aren't doing it to save money, and it's further complicated by the fact that our house is two cottages knocked together but with 2 separate MPANs and domestic circuits, but for us without FiT payments to offset the cost I'm reckoning the batteries will provide around 4KWh/day on average that we would otherwise buy from the grid at £0.20/unit. 365 x .80 is around £300/year so a payback of 20 years, assuming the price of electricity doesn't increase.
But - price is projected to increase by about 80% over the next 20 years so actual payback is much less - plus of course having money sat in the bank is no good at all looking forward to a future of low interest rates and high inflation.
Bottom line - if you have a pessimistic view of the future economy and cash available then batteries could be quite attractive, but if you have a more optimistic view & would need to borrow the money or divert it from other investments that are providing good returns then probably less so.
