Six hours at 7 kW delivers 42 kWh before losses. Seven hours delivers 49 kWh. That can cover modest daily driving, but may not replenish a long working day's consumption.
Is there really a mismatch?
Yes, for drivers who need to replace a lot of energy each night. A 70–80+ kWh battery provides useful range, but a typical single-phase home charger cannot refill it from nearly empty in a six- or seven-hour cheap period.
Many drivers use only a small part of their battery daily. The problem arises when regular long journeys consume more energy than the charger can put back during the discounted hours.
A cheap electricity rate is only useful for the energy you can actually buy at that rate. If the rest must be bought at peak prices or on a public charger, those costs belong in the running-cost calculation.
How much can a 7 kW charger deliver?
Energy equals power multiplied by time. At a steady 7 kW, six hours delivers 42 kWh from the supply; seven hours delivers 49 kWh. A charger delivering 7.4 kW provides 44.4 and 51.8 kWh respectively, before losses.
| Time | Energy from supply | Energy added to battery |
|---|---|---|
| 6 hours | 42 kWh | 37.8 kWh |
| 7 hours | 49 kWh | 44.1 kWh |
| 8 hours | 56 kWh | 50.4 kWh |
| 10 hours | 70 kWh | 63 kWh |
These are calculations, not guaranteed results. Efficiency varies with the car, temperature, charging power and auxiliary consumption. Load balancing, pauses and vehicle charging limits can reduce actual delivery.
What if a 77 kWh battery needs 80% by morning?
Assume 77 kWh of usable capacity, a steady 7 kW charger and 90% efficiency. Gross and usable battery capacity are not always the same; use the correct figure for the actual car.
| Arrive at | Battery energy needed for 80% | Approximate charging time |
|---|---|---|
| 40% | 30.8 kWh | 4.9 hours |
| 30% | 38.5 kWh | 6.1 hours |
| 20% | 46.2 kWh | 7.3 hours |
| 10% | 53.9 kWh | 8.6 hours |
At 30% on arrival, an extra cheap hour could solve the problem. At 10%, seven hours still falls short. From 10% to 100% would take approximately 11 hours under these assumptions, potentially longer in practice.
Needing 80% on departure is different from adding 80% overnight. The starting percentage is essential.
Does Intelligent Octopus Go provide extra cheap hours?
Octopus can schedule smart charging outside the normal 23:30–05:30 household window. However, its current rules give the EV up to six hours of discounted charging per midday-to-midday period. Extra scheduled slots are part of that allowance, rather than a second six-hour entitlement.
Charging beyond the allowance is billed at the peak EV rate, even during the household's overnight off-peak window. Charge Cap can stop charging before that higher rate applies, but may leave the car below its target.
With Ohme, “Prioritise Savings” keeps charging within the allowance; “Prioritise Target” can continue beyond it at peak rates. Other integrations have different controls. Check the current guidance for your exact setup.
Would a seven-hour tariff solve it?
Sometimes. EDF publishes an 11pm–6am off-peak window; E.ON Next Drive Smart publishes midnight–7am. At 7 kW, the extra hour buys another 7 kWh from the supply, roughly 6.3 kWh into the battery in our illustration.
That is meaningful for a small daily shortfall. It cannot make a near-empty 77 or 84 kWh battery fill completely in seven hours.
Compare your postcode quote, daytime rate, standing charge, eligibility, exit fees and solar export arrangement. The best headline rate does not necessarily produce the lowest annual bill.
Are there services without a fixed overnight window?
ScottishPower EV Optimise offers managed charging day or night, excluding 4–8pm. It advertises an 8p/kWh smart charging rate and applies credits to the bill. Its explanation includes VAT treatment, so check the final effective cost. The public product information reviewed does not state an Octopus-style six-hour daily allowance; confirm usage conditions before switching.
A car plugged in from 8pm until morning gives this service longer to work with. That is scheduling flexibility, not a guarantee of continuous charging. A compatible car, home charger and communicating smart meter are required.
OVO Charge Anytime also manages charging without a fixed overnight window. Its standard pay-as-you-go rate from 1 October 2026 is 13.33p/kWh, with a maximum £100 monthly charging credit. Consumption beyond that credit cap is effectively charged at the household rate. Monthly plans have separate kWh allowances.
For high-mileage drivers, caps matter. Confirm exact car and charger compatibility and how much of the month's charging qualifies.
Could I fit an 11 or 22 kW charger?
A charger can only deliver what the property's supply, installation and car allow. A higher-rated wallbox on ordinary single-phase supply does not automatically give the car 11 or 22 kW.
The Ioniq 5 supports roughly 11 kW AC charging, depending on version. Reaching that needs a suitable three-phase supply and charger. A 22 kW wallbox would still be limited by the car's onboard charger.
At 11 kW and 90% efficiency, six hours could add about 59.4 kWh. That can change daily charging substantially, but cost a supply upgrade with the network operator and electrician before treating it as an economical solution.
Why can winter make the shortfall worse?
If the car uses more energy per mile in cold weather, the same commute needs more kWh replaced. Heating, road conditions and driving speed can affect consumption. Charging losses and auxiliary use can also change.
Use observed winter efficiency. For illustration, a 150-mile day at 3 miles/kWh uses 50 kWh from the battery. Replacing it at 7 kW and 90% efficiency takes about 7.9 hours. At 4 miles/kWh, the same mileage needs about 6 hours.
These figures illustrate sensitivity; they are not predictions for a particular Ioniq 5 or route.
What does buying some peak-rate charging do to the cost?
Suppose a day's driving uses 50 kWh from the battery. At 90% charging efficiency, replacing it requires about 55.6 kWh from the supply. Six hours at 7 kW covers 42 kWh; roughly 13.6 kWh remains.
Using illustrative prices of 8p cheap and 30p peak, the charging costs about £3.36 plus £4.07: £7.43 in total, or roughly 13.4p per imported kWh averaged across the session. Buying all 55.6 kWh at 8p would cost about £4.44.
The shortfall adds approximately £3 on that day. Repeated across 220 similar working days, that is roughly £660 extra. These are illustrative rates and driving assumptions, not a quote or a claim about every EV owner. Standing charges are excluded.
Can solar or a home battery cover the missing charge?
Solar can help when the car is home during surplus generation. A commuter's car may be away during useful daylight, particularly in winter, so panels are not an automatic answer to an overnight shortfall.
A home battery can shift electricity into other hours, but capacity, discharge power and losses still apply. A 9.4 kWh battery cannot supply a missing 20–30 kWh from one cycle. Buying substantial storage just to feed the car needs a separate financial assessment.
Check controls: EV charging can drain storage intended for the house. An EV-only charging discount does not necessarily give cheap electricity for charging a home battery.
What should a high-mileage driver do first?
- Record arrival charge and required departure charge for a normal working week.
- Check actual overnight power, delivered kWh and interrupted sessions.
- Use real winter consumption to calculate daily energy needs.
- Compare six-hour charging plus peak-rate top-ups with a longer-window or flexible service.
- Consider reliable workplace charging, public top-ups or three-phase charging where practical.
If the shortfall is occasional, some peak-rate home charging may be simpler than changing everything. If it happens daily, choose the arrangement around the daily requirement.
What needs to be explained more clearly?
The unit price, charging hours and charger power should be discussed together. A low pence-per-kWh figure does not tell a driver whether the car will be ready for tomorrow's work.
A client with an Ioniq 5 raised this because his work journeys required more morning charge than his cheap window delivered. His exact battery capacity and logs have not been verified: the examples above are illustrative rather than measurements of his car.
Ask how many kWh your working day needs, how many the cheap window can replace, and what the shortfall costs.
Sources and tariff checks
Supplier information checked 3 October 2026. Rates, integrations and terms can change; confirm your own quotation and eligibility. All calculations use the assumptions stated.