# Your EV as the battery vs a static home battery — which pays?

> Two ways to store cheap energy and spend it through the expensive hours: use the EV you already own as the battery — what V2L lets you do — or buy a dedicated home battery, what you would install. They answer the same question with very different money, effort and certainty. This page frames the decision; the calculator runs the numbers for your own tariff and vehicle.

## Your EV as the battery (V2L)

You spend little — a changeover kit and an essential board, not a battery — because the expensive part, the battery, is the car you already own. The trade-off is availability and scope: the car must be home and charged through the peak hours, it powers a small essential board rather than the whole house, and every kWh you draw imposes wear on a traction battery that is costly to replace. It pays back fast when it pays back at all, but it cannot save on a day the car is away.

## A static home battery

You spend a great deal upfront — typically several thousand pounds installed — for a unit that is always home, fully automatic, and sized to cover more than a handful of essential circuits. Because it is not tied to your driving, it captures the cheap-rate saving every day, and its warranty throughput is designed for daily cycling. It pays back slowly, but over a long horizon it can net more than a cheap V2L kit precisely because it never misses a day.

## Payback is the wrong test — net cost over the horizon is the right one

A £40 V2L kit that pays back in months can still net less over ten years than a £4,000 battery that pays back in years, because the battery saves on far more days and far more load. The calculator therefore ranks the options on net £ over your chosen horizon (optionally discounted), not on which pays back first — and it shows the payback too, so you see both.

## Where each one wins

V2L tends to win when the car is reliably home through the peak hours, the kit cost is low, and you only need to cover essentials. A static battery tends to win when the car is often away, when you want whole-of-evening cover without manual transfer, or when your horizon is long enough for daily saving to overtake the higher upfront cost. Many households sit between the two — which is what the comparison table on the tool is for.

> Both routes involve fixed electrical work that is notifiable and must be designed, installed and tested by a competent person to the current edition of BS 7671 — a V2L changeover arrangement and a battery installation alike. This page compares the economics and the trade-offs; it is not an instruction to carry out either installation.

Run both options on your own numbers: https://v2lworkshop.co.uk/affordability. The method behind it: https://v2lworkshop.co.uk/affordability/worked-example.

## Sources

- [Octopus Energy — Intelligent Octopus Go](https://octopus.energy/smart/intelligent-octopus-go/) — The cheap whole-home window structure (e.g. 23:30–05:30, whole-home; smart slots car-only). Rates are volatile — verify the current p/kWh.
- [Octopus Energy — REST API (products & unit rates)](https://docs.octopus.energy/rest/guides/endpoints/) — Public, unauthenticated tariff and half-hourly (Agile) unit rates — the source behind this page's optional “Connect Octopus for live rates” button. Octopus is the only supplier currently verified and integrated here; every other supplier stays manual or preset.
- [Ofgem — energy price cap](https://www.ofgem.gov.uk/energy-price-cap) — Regional unit rates and standing charges that bound a standard-rate baseline.
- [GOV.UK — Electric vehicle smart charge point regulations](https://www.gov.uk/guidance/regulations-electric-vehicle-smart-charge-points) — Default-off charging schedules and the randomised start delay that can disrupt a fixed-window plan.
- [myenergi — Zappi ECO/ECO+ charge rates](https://support.myenergi.com/hc/en-gb/articles/5780558509201-ECO-ECO-charge-rates-in-a-three-phase-zappi) — An example of a charger's minimum controllable charge current — confirm your own model against its manufacturer help page, never a forum.

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_Last reviewed: 2026-06-18. Written against: BS 7671:2018 + A4:2026. Education, not project-specific design advice; standards cited by reference only._