Start by assuming your charger is fine. In most cases it is delivering exactly what it was asked for, and the lower number is inside the car. There are seven realistic causes of slow home charging, and they are worth checking in the order below — because the first one explains the majority of cases and costs nothing to rule out, while the expensive fix is near the bottom.
1. The car’s onboard charger is the real ceiling
This is the answer most of the time, and it is the one nobody mentions when they sell you a charger.
AC electricity from your wall cannot go into a battery. It has to be converted to DC, and the converter doing it — the onboard charger— lives inside the car. Whatever that converter is rated for is the hard ceiling on home charging, no matter what is bolted to your wall. A wall charger is a switch and a safety interlock; the car does the conversion.
Published figures, from manufacturers’ own pages, to show the spread:
- Kia EV6 (2026)— Kia’s specification table states “Onboard Charger Power: 10.9 kW” on every trim.
- Nissan Leaf (2026) — Nissan’s press kit publishes a 7.2 kW onboard charger standard on S+, SV+ and PLATINUM+.
- Nissan Leaf (2025, outgoing)— a “6.6 kW onboard charger (6.0 kW output)”, with Nissan’s own 240V charging estimate of about 11.5 hours.
- Volkswagen ID.4 (2026)— VW publishes AC charging “up to 11 kW with the available home wall charger”.
- BMW— BMW’s i4 charging article gives up to 9.6 kW on a 240V, 40A circuit, and builds both its included cable and its own Wallbox around that figure.
Now the arithmetic that matters. 40 amps at 240 volts is 9.6 kW. 48 amps is 11.5 kW. A 2026 Leaf rated at 7.2 kW draws 7.2 kW from a 40-amp charger and 7.2 kW from a 48-amp charger — which is 30 amps, not 40. If you measured your session and got “only” 30 amps, the car is working perfectly and so is the charger.
How to check yours:the owner’s manual charging section, the manufacturer’s specification page, or simplest of all, the charging power the car reports on its own screen while plugged in. That last number is the measured truth for your vehicle.
2. The charger is set lower than it could be
The second-most-common cause, and the cheapest to fix: many chargers ship with an adjustable output and a conservative default, or were dialled down at install to suit a smaller circuit.
Check the charger’s app, buttons or DIP switches for a current setting. If it is on 16 or 24 amps and your circuit supports 40, that is your whole problem. Do not raise it without knowing the circuit: code sizes a continuous load at 125% of its draw, so a 40-amp setting needs a 50-amp circuit and a 48-amp setting needs 60. Our amps and circuits guide covers the sizing.
Also check the car for a charging-current limit. Several EVs let you cap the amps per location, which is a useful feature and an easy thing to have set once and forgotten.
3. The circuit is smaller than you think
Read the number on the breaker handle rather than inferring it from the receptacle.
A 30-amp circuit permits 24 amps continuous, which is about 5.7 kW — Tesla publishes exactly that figure for its Mobile Connector on NEMA 14-30 and 10-30 outlets, against 32 amps and 7.6 kW on a 14-50. If someone adapted a dryer outlet for your charger, 24 amps is the correct and expected result, not a fault. Our guide to charging from a dryer outlet covers that case in full.
And if you are on a standard 120V household socket, you are on Level 1: roughly 1.4 kW, a few miles of range per hour. That is not slow charging, that is a different tier of charging. Our types of chargers guide sets out the levels.
4. It is cold
If charging got slower in November and nothing else changed, this is almost certainly it.
A cold battery accepts charge more slowly as a matter of chemistry, and the car diverts some of the incoming power into warming the pack instead of filling it. The energy is not wasted — a warm pack charges and drives better — but the kWh landing in the battery per hour genuinely drops. On Level 1 the conditioning load can eat most of the charging rate, which is why a 120V cord that coped in summer can lose ground overnight in January.
Nothing to fix here, and nothing to buy. Our cold-weather guide covers what helps (plugging in sooner, preconditioning while still plugged in) and what does not.
5. A schedule, a charge limit, or a utility program
Four settings that look like slow charging and are not:
- Scheduled charging in the car. Plug in at 7pm, car starts at midnight, and at 6am you find it unfinished. Nothing is slow; it started five hours late.
- A charge limit. An 80% cap will look like a session that stops early. Our battery health guide covers why that cap is usually a good idea.
- Utility managed charging. If you enrolled in a program that pays you to let the utility shift or throttle your charging, it is doing that. Worth re-reading the terms.
- Departure-time optimisation. Some cars deliberately stretch a charge to finish just before you leave, which is gentler on the pack and indistinguishable from slowness if you did not know it was on.
6. Load management is throttling the session
If your charger has a sensor on the panel’s main feed, it is supposedto reduce the car’s draw when the house is drawing hard. An electric dryer, an oven and a heat pump running together is exactly when it will back the car off — and that is the feature working, not failing.
The tell is a session that is slow early in the evening and fast after midnight. Most load-managing chargers report this in their app. If it is throttling all night, the panel headroom may genuinely be the constraint. Our load management guide explains the mechanism, and the 100-amp panel page covers living with a tight service.
The same applies to power sharing between two chargers on one circuit: two cars plugged in means each gets a share.
7. A connection is degrading — check this one by hand
Last on the list by likelihood, first on the list by seriousness. Put your hand on the plug and the receptacle after an hour of charging.
A NEMA 14-50 receptacle carrying 40 amps continuously for six hours a night is a far harder duty than the oven or dryer load most receptacles were designed for. Contacts loosen, loosen contacts run warm, warm contacts oxidise, and oxidised contacts run warmer. A cheap residential-grade 14-50 under sustained EV load is a known melting hazard; an industrial-grade receptacle is the fix, and it is pick two below.
Warm is a warning. Hot, discoloured, scorched or loose is a stop.Turn the breaker off and get an electrician. Do not treat this as a charging-speed question. For a new install, hardwiring removes the receptacle from the equation entirely — and sidesteps the GFCI conflict behind most nuisance tripping, since NEC 210.8(A) and 625.54 attach GFCI requirements to receptacles rather than to hardwired equipment. See plug-in versus hardwired and NEMA 14-50 outlets.
A five-minute diagnosis
- Read the car’s reported charging power while plugged in.Compare it against your car’s published onboard-charger rating. Equal? Nothing is wrong — the car is at its ceiling and no charger will beat it.
- Compare it against the charger’s setting. Lower than both? The charger is dialled down, or something is throttling.
- Read the breaker. Confirm the circuit size, and whether 24 amps is actually the correct answer for it.
- Check for a schedule, a charge limit and a managed-charging enrolment.
- Touch the plug. If it is warm, stop here and call an electrician.
The short answer
Find your car’s onboard-charger rating before you buy anything. If the car is at its ceiling, slow charging is a specification rather than a fault and a bigger charger is money on a 60-amp circuit you do not need. If the charger or the circuit is the lower number, raising the charger’s setting is usually free and a 40-amp unit is usually enough. And if the plug is warm, that outranks everything else on this page.
