Real-World Charging: Why the Numbers Rarely Match the Spec Sheet
Earlier this year, Auto ExpressAuto Express ran a comprehensive test at a high-power charging site in Braintree, Essex. Using ultra-rapid 350 kW DC chargers in real-world conditions, they put a wide range of electric cars to the test. The results were eye-opening.
While some EVs briefly hit their peak charging speeds, the majority didn’t. For example:
- The Porsche Taycan came closest, peaking at 282 kW against a claimed 320 kW, adding 60% charge in just 15 minutes.
- The Tesla Model Y managed only 145 kW of its 250 kW potential.
- The Peugeot E-3008, rated for 160 kW, struggled to pull more than 13 kW and took nearly 40 minutes to reach 60% charge.
This wasn’t a technical fault with the chargers or the cars, it's simply how EV charging really works.
What Actually Controls Charging Speed?
Despite what the charger advertises, it's your car’s internal systems, specifically the Battery Management System (BMS) and onboard computers that dictate how fast it can charge.
Here’s what affects charging speed in the real world:
1. The Battery’s State of Charge (SoC)
EVs charge fastest when the battery is low, typically between 10–50%. As the battery fills up, the BMS gradually slows the charge to protect battery health. Above 80%, charging rates drop dramatically.
Think of it like filling a glass, you can pour quickly at first, but need to slow down as you get to the top.
Think of it like filling a glass, you can pour quickly at first, but need to slow down as you get to the top.
2. Battery Temperature
EV batteries work best in a “Goldilocks zone” of roughly 20–30°C. If the battery is too cold or too hot, the BMS will limit charging speed to avoid damaging the cells.
This is why some EVs offer battery preconditioning, warming or cooling the battery before fast charging to improve performance.
3. Your Car’s Maximum Charging Rate
Each EV has a maximum DC charging rate, and it won’t exceed this no matter how powerful the charger is. For example, if your car tops out at 125 kW, it will never pull more than that, even from a 350 kW charger.
4. Charger Load and Infrastructure Limits
At busy charging locations, multiple vehicles may be sharing power from the same source. Some chargers balance output across vehicles, which can reduce your available speed. Local grid limitations can also play a role; especially in rural or high-demand areas.
5. Software and Smart Charging Logic
Your EV and the charger are in constant communication. The car requests power, the charger responds, and the system adjusts in real time based on conditions like battery temperature, SoC, or grid availability.
How Fast Can My EV Charge?
Understanding that peak charging speeds are only possible in ideal conditions and often for just a few minutes can help set realistic expectations.
To get the best results:
- Use battery preconditioning if your vehicle supports it.
- Avoid high-traffic chargers during peak times to reduce the chance of power sharing.
- Check real-world data from ClearWatt’s instant EV Check Plus Report or our EV Health Test app rather than relying on manufacturer specs alone.
Even the fastest public DC charger is only part of the equation. The real limit on charging speed comes from your car and the surrounding electricity grid strain. Factors like battery design, software, temperature, and State of Charge (SoC) all influence how much power your vehicle can safely accept at any given moment.
Understanding these variables not only helps you charge smarter; it also gives you a clearer picture of what to expect from your EV in day-to-day use.