Home battery with an electric car: what changes?
With a car on the drive, a planned battery saves more, not less. Across 20 modelled homes over 34 autumn days on Octopus Agile, a planned 9.5 kWh battery saved the typical home £23.89 over the same battery left to itself with a car plugged in each evening, and £13.03 with no car. When the car charges matters more: on Octopus Go, its charging added £11.64 to the average bill on a night timer, and £32.34 plugged in at teatime.
A car gives a planned battery more to do.
The same homes three ways: with no car, with a car plugged in at a random half hour between 5pm and 8:30pm, and with the same charging on a timer from 00:30. In each, the battery left to itself against the battery Orza planned every half hour, on the home’s own tariff.
| What planning would have saved, typical home, 34 days | No car | Car, plugged in at teatime | Car, on a night timer |
|---|---|---|---|
| Agile, export unpaid | £13.03 | £23.89 | £15.76 |
| Go, export unpaid | £9.99 | £20.25 | £11.94 |
| Flux | £28.60 | £23.98 | £26.96 |
The middle home of 20, 3 September to 7 October 2026: what the battery left to itself cost, less what the battery planned by Orza cost, on the same home, car and days. Energy only: standing charges are left out. Prices as Octopus published them for North West England.
- Left to itself, a battery empties into the carA car plugged in at teatime draws up to 7 kW, and a battery set to cover the house covers the car too, at whatever the hour costs. In the middle home the battery gave out 123.1 kWh in the 34 days with a car, against 109.6 kWh without.
- Planned, the battery is filled for itAcross all 20 homes on Agile, planning would have saved £486.04 with a teatime car against £331.28 without. The most any plan could have saved, knowing every price, cloud and car in advance, was £572.98 with the car and £368.84 without.
- On Flux, a car takes some of the exportFlux pays most for export from 4pm to 7pm, and a battery planned for it sells then. A car charging in those hours needs power the battery could otherwise have sold: it would have saved £509.06 across the 20 homes with a teatime car, against £596.27 with none.
Orza replans your battery every half hour around your tariff’s prices, car or no car.
Tell it when the car charges and the plan has the battery ready. Free, with no card: an email and a password, then an example home to look round. Connect your battery when you’re ready, or never. It starts in Monitor only, and nothing is sent to it until you choose.
A night timer cut what the car added to the bill.
The same sessions, the same days and sizes, moved from a teatime plug-in to a timer from 00:30. What the car added to the average home’s bill over the 34 days:
| What the car added, average home, 34 days | Plugged in at teatime | On a night timer |
|---|---|---|
| Agile, battery planned | £45.05 | £31.06 |
| Go, battery planned | £32.34 | £11.64 |
| Flux, battery planned | £43.18 | £37.04 |
| Agile, battery left to itself | £52.79 | £32.99 |
| Go, battery left to itself | £38.21 | £13.08 |
Average of 20 homes, 3 September to 7 October 2026: the home’s energy cost with the car, less the same home’s without it, the battery run the same way in both. Sessions of 4 to 14 kWh at 7 kW on about half the days. Standing charges left out.
- On Go, the timer did most of the workGo’s cheap hours are at night, and a timer from 00:30 starts inside them: £11.64 against £32.34. How Go, Agile and Flux compared over a whole year, without a car.
- On Agile, the cheap hours moveAgile’s cheapest half hours shift from night to night, so a fixed 00:30 start does not always catch them: £31.06 against £45.05. When Agile was cheap and dear on a real home.
- Planning helped most where the car was least predictableA teatime plug-in, at a different time each day, gave planning the most to save on every tariff but Flux.
A night rate, plus cheap slots that follow the car.
Octopus’s page gives the whole home a cheap rate for six hours every night, 23:30 to 05:30, and the car up to six hours of smart charging in every 24. Those hours may fall outside the night, and when they do the whole home gets the cheap rate too. The figures above aren’t for this tariff: its extra slots follow the car, which the runs have no record of.
- A battery set to cover the house covers the car tooWhen the car charges in a slot by day or in the evening, a battery left to itself empties into it just when the grid is cheap, and that charge is gone when the rate goes back up.
- Overnight, the plan works around the carOrza reads your rates from Octopus and plans to 23:30 to 05:30, filling the battery in the cheap hours and keeping it for the day. Add the car under Appliances with the times it charges, and the plan expects the extra power and has the battery ready.
- By day, a Hold keeps the battery out of itThe extra slots aren’t known in advance, so the plan doesn’t count on them. If the car tends to charge at set hours, put a Hold for them on your Schedule: under Automatic control the battery keeps its charge and the car draws from the grid. If no slot comes, the house draws from the grid at the day rate for those hours.
Intelligent Octopus Go as Octopus’s page gave it on 3 November 2026: 6.5p a kWh in those hours, with bump charges at the day rate. Automatic control and the Schedule are for the makes whose clouds let Orza send to the battery.
Real meter readings, a modelled roof, battery and car.
Each home is a real London household’s smart meter readings, with a modelled 4 kWp roof and a 9.5 kWh, 5 kW battery, under the weather and Octopus prices of five weeks of autumn 2026. The households had no cars when their meters were read, so the car is added to each one.
The car added to each home
- A 7 kW home chargerSessions of 4 to 14 kWh, on about half the days, a little less often at weekends.
- Plugged in at teatimeAt a random half hour from 5pm to 8:30pm, charging straight away. The hard case: a different hour each day.
- Or on a night timerThe same sessions, starting at 00:30.
- The limitsTwenty modelled homes over 34 days of autumn is one stretch of weather and prices, not a year, and not your home. Winter would give a battery less sun to store.
A battery, a car and a tariff.
What owners ask next, answered from the same homes where it can be.
All our guidesGet more from your battery
How Orza is tested
Are these real homes?
Their electricity use is: 20 real households’ smart meter readings, from Low Carbon London (UK Power Networks, CC BY 4.0). The roof, the battery and the car are modelled, under the weather and the prices Octopus published for 3 September to 7 October 2026.
Should I charge my car from my home battery?
Not as a rule. A 9.5 kWh battery holds less than a long session, and some energy is lost going in and out of it: a real 27 kWh battery gave back 82.1% at the inverter. Where night power is cheap, the car is usually better charged straight from the grid then. Left to itself, a battery empties into a car plugged in at teatime, and the car still added £52.79 to the average home’s bill on Agile. How much a battery loses on the way.
Does Orza work with Intelligent Octopus Go?
Yes: it plans the battery around the 23:30 to 05:30 hours. Octopus’s extra slots for the car aren’t known in advance, so the plan doesn’t count on them. A Hold on your Schedule keeps the battery out of the car at the hours it tends to charge. What the plan does with the car.
Which Octopus tariff is best with a car and a battery?
On these homes, with the car on a night timer, Go left the lowest bill: £607.19 across the 20 homes over 34 days, against £673.70 on Flux and £1,071.81 on Agile. With the car plugged in at teatime, Flux did: £796.38, against £1,021.31 on Go and £1,351.53 on Agile. Export was unpaid on Go and Agile here, and Flux pays for it. Over a whole year without a car, the ranking is in Go, Agile or Flux with a battery.
Do I need a bigger battery if I have an electric car?
We didn’t run other sizes with a car. Without one, each kWh added saved less than the one before, and the gain from a bigger battery grew with how much a home used. A car adds to that use. Four battery sizes on a year of homes.
Does a battery left to itself work with a car?
It does what it always does: stores spare sun and empties into whatever the house is using, car included. Planning the same battery would have saved £486.04 more than that across the 20 homes with a teatime car on Agile, against £331.28 with no car. The ways to schedule a battery, compared.
What does Orza cost?
Nothing right now: everything is free while we spread the word, and no card is needed to join. Paid tiers will come later, and there will always be a free version. If you already have a battery, Orza plans it every half hour for your own tariff.
A battery and a car? Make it the planned battery.
These homes are modelled. Connect yours in Monitor only and Orza shows, from your own readings, what its plan would have saved with the car on the drive, and sends your battery nothing.