【EV Charging 101】Fast vs. Medium Charging, Battery Health & Cable Buying Tips

EV charging starts with the standard. The vast majority of electric vehicles in Hong Kong adopt the European standard. While some Japanese brands use the CHAdeMO standard for fast charging, they are becoming increasingly rare, so we will focus on the European standard this time.

The European standard is divided into AC (Type 2, for Medium Charging) and DC (CCS2, for Fast Charging). When you open the charging cover on your car, you will see two plastic caps (some models only have one). If you are only using Type 2 medium charging, you only need to open the top cap. If you need CCS2 fast charging, you must open both caps to insert the charging connector.

To understand how charging works, you can imagine it as "filling a bucket with a water hose." The kW represents the hose: the thicker the hose, the higher the flow rate, and the faster the bucket (battery) is filled. So, what exactly are the terms "Slow Charging," "Medium Charging," and "Fast Charging" that people often use?

In theory, a higher kW rating represents a faster rate of power transfer. However, should you choose a charging station based on the kW value alone? Why do some medium charging stations indicate 7kW, 22kW, or even higher?

This is because AC (Medium Charging) involves Single-Phase and Three-Phase power. For easier understanding, imagine Single-Phase as one water hose supplying water, while Three-Phase has three hoses supplying water simultaneously. Let’s look at the following calculation methods.

Single-phase electricity vs. three-phase electricity

• Single-phase electricity: Powered by only one wire.

Calculation formula: 220V x 32A = 7kW

• Three-phase electricity: Power is supplied by three wires simultaneously.

Calculation formula: 220V x 32A x 3 = 21kW - ​​22kW

However, a high kW rating does not necessarily mean faster charging speeds; it also depends on the vehicle's compatibility. For example, if a vehicle only supports single-phase charging, it will still only receive a maximum of 7kW even when using a 22kW charger.

When charging with AC (Medium Charging), the vehicle acts as a "conversion station." It relies on the On-Board Charger (OBC) to convert the AC power from the wall into the DC power that the battery can absorb. Therefore, it is limited by the phases and power capacity of the OBC.

In DC charging (Fast Charging), the charging pile itself is a massive "conversion station." It directly injects high-power direct current into the battery, bypassing the OBC inside the vehicle. As a result, the concept of single-phase or three-phase does not exist in DC fast charging; there is only the matter of matching power (kW), voltage (V), and current (A).

Output limits of the charging pile

For example, if a fast charging pile is labeled as 50kW / 500V / 125A, it means the maximum current it can provide is only 125A.

Vehicle battery voltage architecture

There are currently two mainstream voltage architectures for electric vehicles: 400V and 800V. The 400V platform includes the Tesla Model 3 / Y and most existing EVs. The 800V platform is beginning to appear in high-end models, such as the Zeekr 009 / 7X, Porsche Taycan, and Hyundai IONIQ 6.

To calculate the speed, we can use the following formula:

Example 1

Example 2

All electric vehicles are equipped with a Battery Management System (BMS), which means the vehicle requests power based on the battery's temperature and state of charge. When the battery level exceeds 80%, the BMS instructs the charging pile to "narrow the hose," causing the output power to gradually decrease. Additionally, a single charging pile often provides two fast-charging plugs. If both are used simultaneously, the power will be split; for example, a 250kW pile's maximum power would drop to 125kW per plug. A third factor is battery temperature—if it gets too high, the charging speed will also be restricted.

The theory that "fast charging damages the battery" is technically valid because the heat generated during charging accelerates the internal chemical decomposition of the battery. Furthermore, if the charging speed is too fast, lithium metal may accumulate, which in severe cases can form "dendrites" that lead to short circuits.

However, there is no need for excessive concern, as modern EV battery temperature control technologies—such as the Battery Management System, cooling systems, and pre-conditioning functions—are now extremely precise. According to a 2026 research report from Geotab, EVs that frequently use fast charging have an average annual battery degradation rate of 3%, with an estimated 76% capacity remaining after 8 years. In contrast, EVs primarily using medium charging have an annual degradation rate of 1.5%, with an estimated 88% capacity remaining after 8 years. As shown, even EVs frequently using fast charging retain 75% capacity after 8 years, which is still higher than the 70% threshold claimed by most manufacturers.

If you plan to use medium charging for your EV, a charging cable is definitely a must-buy item. But how do you choose the right one? it depends on the following factors:

• Single-Phase / Three-Phase

As mentioned above, single-phase uses only one wire for power supply, while three-phase uses three wires simultaneously. First, you should understand whether your vehicle supports single-phase or three-phase charging. You can distinguish this by observing the vehicle's charging socket: if there are metal pins inside the middle-right hole and the two bottom holes (L1、L2 & L3), the vehicle supports three-phase charging. If there is a metal pin only in the middle-right hole（L1）, the vehicle only supports single-phase charging.

• Current

As the name suggests, current is the flow of electricity; the higher the number, the faster the current flow. Charging cables are generally divided into 16A and 32A. Different types of charging cables are available to match different phases.

Generally, charging cables are labeled with the phases and current they support. When buying a cable, check the label on the plug; for example, "32A 3P" indicates a 32A three-phase charging cable, while "32A 1P" represents a 32A single-phase charging cable.