Fast or slow charging: what really affects an EV's battery?

The world of electric mobility is constantly evolving, and with it comes growing curiosity—and often confusion—about how to best care for an electric car's battery. One of the most frequently asked questions among owners (or aspiring owners) concerns charging: is it better to opt for slow charging or rely on the convenience of ultra-fast charging stations ? This choice is based not only on practical considerations related to available time, but also on direct implications for the health of the battery, which is the heart—and most expensive component—of every electric vehicle.

In this article, we'll take a detailed look at what actually happens to a battery during slow or fast charging, what factors influence cell aging, and how to strike the right balance between daily needs and battery pack longevity. We'll discover that the answer isn't always so clear-cut, and that the "true impact" of charging depends on a combination of often overlooked factors.

What is slow charging?

Slow charging is the most common and, in many ways, the most gentle way to recharge a battery. Unlike rapid or ultra-rapid charging, this method delivers power at a lower rate, making it ideal for situations where the vehicle is stationary for several hours, such as overnight in the garage or during the workday.

The heart of slow charging lies in its alternating current (AC) operation. When you plug your car into a standard household outlet, a wallbox installed at home, or many public charging stations, you're using this type of charging. Essentially, the electricity coming from the grid or charging station is AC, but the car battery can only store direct current (DC). This is where the vehicle's on-board charger comes in: it's responsible for converting AC to DC, thus enabling energy storage.

There are several nuances of slow charging. The most basic involves plugging the car into a standard household socket , often with a cable equipped with a small "control box" for safety. This is the slowest option, with power levels rarely exceeding 3.7 kW, and charging times can last a whole night or even longer. A step up is represented by home wallboxes or public AC charging stations. These solutions offer higher power levels, typically from 7.4 kW to 22 kW (the latter requires a three-phase power supply at home), significantly reducing charging times compared to a domestic socket, but still taking several hours for a full charge.

Once the car is connected via cable (in Europe, the most common connector is Type 2 ), a communication phase takes place between the vehicle and the charging point. This "dialogue" is essential for establishing the maximum safe power output, protecting both the car battery and the electrical system. Only after this check does the energy begin to flow and is converted by the on-board charger before being stored in the battery.

The advantages

The benefits of slow charging are numerous. First, charging at a lower power generates less heat and reduces chemical stress on the cells, helping to preserve their longevity . Economically , it is often the most advantageous option, especially if you can charge at home at night while taking advantage of lower electricity rates. Its convenience is undeniable: it allows you to "fill up" while the car is parked for long periods, such as overnight or while you're at work. Finally, it requires a less complex and expensive electrical infrastructure to install than fast charging solutions.

Depending on battery capacity and available power, a full charge can take 5 to 12 hours , or even longer. This makes it less practical for a quick top-up during a trip, where rapid or ultra-rapid charging stations (which supply direct current, not alternating current) are essential.

What is fast charging?

Rapid charging, on the other hand, is the solution designed to minimize waiting times , offering a refueling experience closer to that of a traditional combustion engine car. This mode is primarily found at public charging stations along highways, service areas, and in strategic urban centers. It works by supplying direct current (DC) directly to the vehicle's battery. With rapid charging, the AC/DC conversion occurs within the charging station itself. This bypasses the vehicle's on-board charger, which typically has lower power limits, and sends a much more powerful flow of energy directly to the battery.

Rapid charging stations, also known as " Fast Chargers " or " Ultra Fast Chargers ," offer power outputs starting at 50 kW and can reach well beyond 350 kW, with some stations even exceeding 400 kW. For example, a 100 kW station can charge a medium-capacity battery (60-70 kWh) up to 80% in about 20-30 minutes, depending on the car model and environmental conditions.

The most common fast-charging connectors in Europe are the CCS Combo 2, which has become the reference standard, and in some cases the CHAdeMO, although the latter is less common for newer models. These connectors are designed to handle high power, and the cables are often thicker, sometimes even liquid-cooled in ultra-high-power stations to ensure safety and efficiency.

The benefits

The advantages of fast charging are clear. The most obvious is its speed: it allows you to recover hundreds of kilometers of range in just a few minutes, making long journeys much more feasible and alleviating so-called " range anxiety ." It's an ideal solution for those who travel long distances, have limited rest periods, or don't have the option of installing a private charging station. Its widespread presence along major roads and in service areas makes it a key component for long-range electric mobility.

However, there are some factors to consider. Fast charging sessions are generally more expensive . Furthermore, although modern technologies have made great strides, extremely frequent and continuous use of fast charging could, in theory, slightly accelerate battery degradation. It's important to note that most modern electric cars are designed to handle these stresses, and the most recent studies often show no significant differences in degradation between batteries charged predominantly with DC and those charged with AC, provided the manufacturer's recommendations are followed and the battery is not abused by systematically charging to 100% or with the battery almost flat.

Another peculiarity is that fast charging, to optimize battery health and charging speed, tends to slow down significantly once a certain percentage (often 80%) is exceeded: for this reason, 100% charging is rarely possible with these columns, since the last 20% would take a disproportionate amount of time.

It is clear, therefore, that there is no one solution better than another, but depending on the situation and your needs, it may be better to recharge a battery slowly or more quickly.