Charger-side or car-side: which one controls your off-peak charging

Charger-side scheduling means the charge point itself decides when to start and stop, based on an instruction it pulls from your tariff provider. The charger needs an internet connection and runs an app that logs into the tariff provider's systems, usually over what's called an API, to find out when your off-peak window opens and closes.

How the charger gets its schedule

Once the app is linked to your account, it checks the tariff provider's current off-peak times each day. This matters because some tariffs move their off-peak window around, or run a different window at weekends, and a charger that only checked once at setup would keep charging to the old times.

With the link in place, you plug in whenever it suits you and the charger holds off starting until the off-peak window opens, then switches on automatically. Most apps let you override this for a one-off full charge, and some let you set a minimum charge level that's topped up even outside the off-peak window if you need the car ready early.

What happens when the link breaks

The connection between charger and tariff provider can fail: the tariff provider's servers go down, your home broadband drops, or the app's authorisation simply expires and needs logging in again. When that happens, the charger stops receiving the off-peak times it needs and falls back on whatever default behaviour is built into it.

The Electric Vehicles (Smart Charge Points) Regulations 2021 require every smart charge point sold in Great Britain to come with a default setting that avoids charging at peak demand times unless you tell it otherwise; these regulations do not extend to Northern Ireland. That default is what the charger falls back to if its link to your tariff stops working, so a broken integration doesn't usually mean charging at full peak rate, but it does mean the charger is no longer following your actual tariff's window.

It's worth checking the charger's app occasionally to confirm it still shows a connected status with your tariff provider, particularly after you've changed broadband router, changed your home Wi-Fi password, or switched supplier. A charger that looks like it's charging normally can still be running on its fallback schedule.

With car-side scheduling, the car holds the clock. You set an off-peak window, or a target charging time, in the car's own menu or its manufacturer app, and the car releases current to its battery only once that window opens. Plug in at six in the evening and nothing happens until the set hour arrives, whatever the charger is doing.

Why it works with any charger

Because the schedule lives in the car, this route doesn't care what charger is fitted. A basic, unconnected unit does the job as well as an app-connected one, since the car is the part doing the timing. There's no account to link and no app pairing between charger and tariff to set up or keep working.

What the tariff provider can and can't see

The supplier billing you on the off-peak rate reads what the smart meter recorded. A charge that began at 1am looks identical to the meter whether a tariff app triggered it or the car's own clock did. The supplier can confirm electricity was drawn in the cheap window; it has no way of seeing whether that will keep happening once a clock resets or a setting gets changed.

That gap matters because the car's clock can drift, through a software update, a time zone change, or a daylight saving adjustment that doesn't apply itself. When it does, charging can start outside the window you intended, and the first sign of it is usually a higher bill.

What to check yourself

• Which window is currently set in the car, and whether it needs re-entering after every charge or only once
• Whether the car's clock updates on its own or needs resetting by hand
• Whether the charge limit and the off-peak schedule are set separately, since changing one doesn't always carry across to the other