you can now get a 15kwh battery for £2500, you just need an inverter, say £600, an electrician to install it and some paperwork from your DNO.
We are going well off topic, there is a massive thread on this in home and garden. Please use it.
Link? Assuming this isn't a "50% chance to burn your house down" type battery

I don't think it's too off-topic, for anyone doing decent mileage in an EV, it's going to be a significant chunk of their electricity costs, coupled with the fact that many time-of-use tariffs are aimed towards EV charging (and in some cases even require one).