Why Is My Home EV Charger Charging Slowly? 7 Possible Causes

Plugged in all night, woke up expecting a full battery, and the car’s barely moved. We hear this one constantly, and more often than not the charger itself is doing exactly what it’s supposed to. Something else further down the chain, the car, the cable, the circuit, even a setting buried in an app, is quietly deciding how fast the electricity actually flows.

Seven things tend to come up again and again when we go looking. Not all seven apply every time, obviously, but between them they explain almost every “my charger’s gone slow” call we get.

1. Your Car’s Onboard Charger Is Doing the Limiting, Not the Wallbox

Every EV has its own ceiling for how much AC power it’ll accept, and that number lives in the car, not in the box on your wall. Install a 7kW charger on a car that only takes 3.6kW on AC, and the extra capacity just sits there unused. The wallbox isn’t holding anything back. It’s offering more than the car’s willing to take.

Catches people out all the time, especially with older or entry-level EVs where a 3.6kW onboard limit is pretty normal, even sitting underneath a charger rated for double that. Worth checking your actual vehicle handbook for the real figure before assuming the wallbox is the problem.

2. The Charger Was Never Set Up at Full Output in the First Place

Not every home charger runs at 7kW. Some get installed at 3.6kW on purpose, because that’s what the property’s supply or consumer unit could handle safely at the time, and the homeowner doesn’t always get told there was a ceiling involved at all.

Check your installation paperwork, or just ask whoever fitted it. If your setup’s moved on since then and could now take more, our page on whether you need a new consumer unit for an EV charger walks through what that upgrade actually involves.

3. Load Management Is Throttling It on Purpose

A lot of modern chargers watch how much power the rest of the house is drawing and quietly turn themselves down if things get busy, the oven’s on, the heating’s running, someone’s doing a wash. That’s dynamic load management, and it’s a safety feature protecting your main fuse, not a fault.

Which is exactly why charging speed can swing through the evening depending on what else is switched on. Notice it speeding up once everything else in the house quietens down for the night? That’s almost certainly this.

4. Something’s Off With the Cable or the Connection

A worn, cheap, or simply underrated cable can bottleneck speed even when the car and the charger are both perfectly capable of more. Goes for the tethered lead on the wallbox itself and for any separate Type 2 cable you’re using elsewhere too.

A connection that isn’t fully seated, at either end, the charger or the car’s port, can make the system throttle itself down deliberately to avoid overheating. Worth a quick check before assuming something more serious is wrong. If you switch between a tethered home charger and a portable cable depending on where you’re charging, comparing the two speeds is a quick way to tell whether the cable’s actually to blame.

5. Your Battery’s State of Charge or the Weather Is Slowing Things

Charging tapers naturally as a battery fills, on pretty much every EV, and that’s by design rather than anything going wrong. Climbing from 20% to 80% is usually quicker, proportionally, than crawling the last stretch from 80% to full.

Cold does something similar. Battery management systems often pull charging rate back in low temperatures specifically to protect the cells, which is part of why a charge feels noticeably slower on a freezing night than a mild one, even on the exact same charger, nothing else changed.

6. An Eco or Scheduled Setting Is Quietly Capping It

Plenty of smart chargers let you set a maximum rate through an app, sometimes to save money, sometimes to ease the load on the house’s wiring during certain hours. Easy to set once and forget entirely, then wonder six months later why charging’s slower than it used to be.

Worth a look through your charger’s app for anything capping amperage or output, particularly if the install was done with a specific overnight tariff in mind, where staying under a certain rate keeps you within that tariff’s terms.

7. There’s Actually Something Wrong

Sometimes it genuinely is a fault, and that’s where a proper visit beats guessing over the phone. A relay starting to fail inside the charger. A terminal working loose in the consumer unit. A circuit that’s degraded since the day it was fitted. All three can drag charging speed down, sometimes gradually, sometimes overnight.

Worth thinking back too. Has anything changed about your home’s electrics since the charger went in? Another big appliance added, a consumer unit swapped out by someone else, anything that might be eating into the capacity the charger circuit used to have to itself.

How We Actually Get to the Bottom of It

We don’t start by assuming the charger’s broken, because nine times out of ten it isn’t. First thing we check is the car’s actual onboard charging rate, since that one number rules out a huge chunk of “slow charging” complaints before we’ve even opened the consumer unit.

After that we confirm what the charger’s actually configured to deliver against what it was installed at, check whether load management’s active and whether that explains the pattern being described, and physically look over the cable and connections for wear or looseness. Only once all of that’s clear do we start treating it as a genuine fault that needs fixing.

The Charger That Was “Definitely Broken” in Barnet

Had a call from a homeowner in Barnet dead certain their eighteen month old charger had packed in, since charging had slowed noticeably compared to when it was new. Nothing had actually failed. They’d changed cars a few months earlier, and the new one’s onboard charger simply accepted less than the old one had, 6.6kW instead of 7.2kW. The charger hadn’t changed at all. The car sitting in front of it had.

Ealing was a different story entirely. Charging there had been getting slower over several weeks, not overnight, which is usually the giveaway that something’s actually degrading rather than something external changing. Turned out to be a terminal loosening inside the consumer unit, causing a voltage drop under load. Tightened and torque checked properly, and the problem was gone. That one genuinely needed eyes on it. No amount of guessing over the phone would’ve caught it.

Does Any of This Change at Workplace or Rapid Chargers?

The same ideas apply, just scaled up. Our guides on workplace EV charger installation and commercial EV charger installation cover that bigger picture, where load management across a whole row of bays becomes a far bigger factor than it usually is for one charger on a house.

Worth Getting the Electrics Checked Before This Starts?

Often, yes, particularly if you think something’s drifting rather than sudden. Our guide on preparing your home’s electrical system for an EV charger installation explains what that kind of check actually covers, and it’s worth revisiting even on a system that’s run fine for years if your home’s power use has shifted recently.

How Does This Relate to Installation Time?

Different thing, but related enough to be worth reading together. Our guide on how long EV charger installation takes covers getting the charger fitted in the first place rather than how it performs afterward, but it rounds out the picture if you’re trying to understand your setup end to end.

What Does It Cost to Get This Looked At?

Comes down to what’s actually found, same as any electrical diagnostic. Our page on EV charger installation cost explains how we price things generally, and our guide on EV charger installation labour cost breaks down where labour tends to sit if a repair or upgrade ends up being needed.

Would a Bigger Charger Just Fix It?

Only if the charger’s output was genuinely the bottleneck to begin with. If your car caps out at 3.6kW, a shinier, more powerful wallbox changes nothing, since the car was always going to be the limiting factor whatever’s feeding it. Worth confirming the actual cause before spending money on a part that might not move the needle at all.

Please Don’t Try to Chase This Down Yourself

Opening a consumer unit or chasing a wiring fault isn’t a weekend project, for fairly obvious safety reasons. Our guide on whether you can install an EV charger yourself explains why this kind of work needs a qualified electrician, and the same logic holds for diagnosing a fault, not just fitting the thing in the first place.

Getting It Properly Looked At

Every visit starts the same way, checking the car, the charger’s settings, and the cable, before anyone assumes it’s a fault needing parts. We run a 7 day turnaround once booked, and we’re already past 15,000 installs across the UK, so tracking down what’s actually behind a slow charge isn’t new ground for us. Request a quote and we’ll take an actual look rather than guessing down the phone.

We install and service chargers across Croydon, Barnet, Richmond upon Thames, Ealing, Watford, Westminster, Wandsworth, Waltham Forest, Tower Hamlets, and Sutton, checking things the same way on every single call out, wherever the postcode happens to be.

Not Sure Why Yours Has Slowed Down?

No need to guess from a forum post or brace for the worst. Get in touch through our contact page and we’ll talk through what’s actually likely going on before anything gets booked in.