Why Is My EV Charging Slowly? Full Explanation
Why Is My EV Charging Slowly?
The three hard limits
| Limit | What it means |
|---|---|
| Vehicle's onboard charger (OBC) | Every EV has a maximum AC charging rate built into the car itself. A 22kW home charger cannot make a car with a 7.4kW onboard charger charge any faster than 7.4kW — the car itself ultimately decides how much power it will draw, regardless of what's available upstream. |
| Charge point's output | Your home charger has its own maximum rated output — commonly 7.4kW (32A single-phase) for UK homes, or up to 22kW on a 3-phase supply. |
| Cable's current rating | The cable connecting car to charger has its own maximum current rating (measured in amps, not kW) — and this is the limit most people misunderstand. See below. |
Charging speed is always the lowest of these three — never the average, and never whichever is highest.
Find your vehicle's maximum AC charging speed
Search or filter below for an approximate maximum AC charging rate. This covers the most common EVs on UK roads — figures can vary by trim and model year, so always confirm against your specific vehicle's handbook if you're making a buying decision based on it.
Figures are typical maximum AC (home/destination) charging rates, not DC rapid charging speeds. Always verify against your vehicle's own specification for anything decision-critical.
Understanding cable ratings — the limit people miss
Cables are rated in amps, not kW — the kW figure printed on a cable or in its description is calculated assuming it's used at its intended phase configuration. This is where a lot of confusion comes from, because the same cable can deliver very different power depending on what it's plugged into.
| Cable rating | On single-phase | On 3-phase |
|---|---|---|
| 16A | 3.6kW | 11kW |
| 32A | 7.4kW | 22kW |
This is the catch: a cable marketed or labelled as "11kW" is a 16A cable — it only reaches 11kW when all three phases are being used. If that same 16A cable is used on a single-phase 7.4kW (32A) charger, the cable's 16A rating is now the bottleneck, not the charger — so you'll only get roughly 3.6kW, even though the charger itself is fully capable of 7.4kW and the car may be too.
This exact scenario — a "bigger sounding" 11kW cable actually charging slower on a single-phase setup — is one of the most common genuine causes of unexpectedly slow charging, and it's rarely explained clearly. If your cable is labelled with a kW figure, check its actual amp rating (16A or 32A) printed on the cable or its datasheet, since that's what actually determines the outcome once phase configuration is accounted for. See our full cable ratings guide for the complete amps-to-kW reference.
Dynamic load balancing, explained simply
Think of your home's electricity supply as having a total ceiling — a maximum amount of current your incoming cable and fuse can safely carry at once. Load balancing is a feature built into many chargers that watches how much of that ceiling is already being used by the rest of your home (oven, shower, kettle, immersion heater, etc.) and automatically turns the charger's output down, moment to moment, to avoid going over the top.
The simplest way to tell if load balancing is the cause: does your charging speed fluctuate up and down during a single session, rather than staying at one steady (if low) rate throughout? Fluctuating speed almost always points to load balancing reacting to the rest of your home's usage. A rate that's consistently low from start to finish — never varying — points instead to one of the other causes on this page (cable, vehicle limit, or a software-set cap, covered next).
The car always has the final say — but where is the limit actually set?
It's worth understanding that the vehicle itself always makes the final decision on how much current it draws — this is a deliberate part of the EV charging standard (via the control pilot signal between car and charger), not something the charger can override. But that doesn't mean the charger or its ecosystem has no influence — a software-configured limit can exist in several different places, and it's easy to check the wrong one and conclude there's a hardware fault when there isn't.
| Where a limit could be set | What to check |
|---|---|
| The car's dashboard/infotainment settings | Many EVs let you manually set a maximum charge current or charging power limit — sometimes set low deliberately (e.g. for battery longevity, or leftover from a previous setting) and forgotten about |
| The car manufacturer's app | Some manufacturer apps (for example, adjusting amperage/current sliders) let you cap charging speed remotely — worth checking this matches what you expect, separately from the in-car setting |
| The charger's consumer app | Most smart chargers have a power/current limit setting in their own app, independent of both the car and the electricity supply — this is a common place for a limit to be set (sometimes unintentionally) by whoever last used the app |
| The charger's installer-side configuration | During commissioning, an installer sets the charger's maximum output current to match the circuit and cable that was actually installed. If the installation used a 16A-rated cable or circuit rather than 32A, the installer may have deliberately configured the charger to cap its output at 16A (3.6kW/11kW) to match — this is a legitimate, compliant configuration choice, not a fault, but it's easy to forget was done. If your charger seems permanently capped below what you expected when you bought it, this is worth checking directly with your installer rather than assuming it's a hardware problem. |
Single-phase vs 3-phase — a brief explanation
Most UK domestic properties have a single-phase electricity supply, which caps AC EV charging at 7.4kW (32A) regardless of what charger you install, unless you upgrade your supply. Some larger properties, new-builds, or commercial premises have a 3-phase supply, which allows considerably higher AC charging rates — up to 22kW — provided your charger, cable, and vehicle are all also 3-phase capable. Installing a 22kW charger on a single-phase supply will not give you 22kW charging; the supply itself becomes the limit. Equally, an 11kW or 22kW-capable car plugged into a single-phase 7.4kW charger will only ever reach 7.4kW, however capable the vehicle is. As with everything on this page, the achievable speed always comes down to the specific combination of car, charger, cable, and supply you actually have — not any one component in isolation.
Other conditions that reduce charging speed
Cold batteries
Lithium-ion batteries charge more slowly, and sometimes enter a reduced-current "conditioning" mode, when cold — commonly below around 0-5°C. This protects the cells and is normal, most noticeable on winter mornings after a car has sat outside overnight.
Hot batteries
Less common in the UK, but a battery that's very warm — for example after DC fast charging or hard driving in hot weather — can have its charging rate temporarily reduced to protect the cells.
Battery nearly full
Charging speed naturally tapers as the battery approaches 100%, similar to a phone slowing down near a full charge — this protects long-term battery health and is completely normal.
Scheduled charging and smart tariffs
If you're on a time-of-use tariff such as Octopus Intelligent or similar, the tariff provider may be actively pacing your charging session across the cheap-rate window rather than charging at full speed immediately, even if the hardware is capable of more. Check the tariff app specifically, not just the car or charger.
If speed has dropped permanently rather than varying session to session, and you've ruled out the causes above, it could be a hardware fault.
See our repair & diagnosis guide →Frequently Asked Questions
Why is my 7kW charger only giving me 3.6kW?
The most common cause is an "11kW" charging cable being used on a single-phase supply. An 11kW cable is rated 16A, and 16A only reaches 11kW across all three phases — on a single-phase charger, that same 16A cable caps out at roughly 3.6kW, even though the charger and car may both be capable of the full 7.4kW. Check the amp rating printed on the cable rather than relying on its kW label.
Why does my charging speed change during a session?
This is almost always dynamic load balancing responding to the rest of your household's electricity usage in real time. It's a safety feature, not a fault, and is most noticeable during the evening when other appliances are also drawing power.
My charger always charges slowly, at a consistent low rate — why?
A consistently low rate that doesn't vary during a session points to a fixed limit rather than something reactive like load balancing. Check, in order: the cable's actual amp rating, any charge current limit set in the car's dashboard or app, any limit set in the charger's app, and finally check with your installer whether the charger was deliberately configured with a lower output cap to match the circuit or cable installed.
Will a 22kW charger charge my car faster than a 7kW one?
Only if your vehicle's onboard charger and your electricity supply are both 3-phase and capable of more than 7.4kW. Most UK homes are single-phase, which caps AC charging at 7.4kW regardless of the charger's own rating, and most EVs have an onboard charger below 22kW.
Does the charger or the car decide how much power is used?
The vehicle always has the final say on how much current it draws, as part of the standard communication protocol between car and charger. However, the charger, cable, and supply all set the ceiling the car is choosing from — if any of those is lower than the car's own maximum, that becomes the effective limit instead.