We put PV panels in last autumn (great timing in the northern hemisphere...). Looking at the prices, a 10 kWh battery, which would have made us effectively 'off grid' in terms of our requirements for maybe 9 months of the year, would have more than doubled the cost of the installation, and paid for itself -at the current differential between what the reseller pays us into the 'virtual battery', and what we pay for non-solar-hours consumption- in about 7-8 years. But had a 5 year warranty...

I decided against it, and will retrofit a battery in a couple of years once prices have come down a bit, and power density and longevity have gone up.