Why Doesn’t All the Energy Go Into My EV’s Battery?
When charging an electric vehicle (EV), you may notice that the amount of energy drawn from the grid is higher than what your battery actually stores. This difference is due to charging efficiency losses, which are a normal and expected part of the charging process.
These losses typically range between 10-20%, depending on various factors, including charger type, vehicle system efficiency, and environmental conditions.
What Causes Charging Efficiency Losses?
There are several reasons why not all the energy from the charger makes it into your battery:
AC-to-DC Conversion
If using AC charging (such as a Level 1 or Level 2 charger), your vehicle’s onboard charger must convert AC electricity from the grid into DC electricity to store in the battery. This conversion process is not 100% efficient and leads to some energy loss.
Heat Loss
Electrical resistance in the charging components naturally generates heat, which reduces overall efficiency. In addition, cooling systems may activate to manage battery temperature, consuming extra energy during charging.
Charging Equipment & Cable Resistance
The efficiency of the charger, connectors, and cables also plays a role. Longer or thinner charging cables can introduce higher electrical resistance, leading to additional losses.
Battery Management & Safety Systems
Modern EVs have built-in battery management systems (BMS) to regulate voltage, monitor battery health, and optimize long-term performance. These systems consume small amounts of energy during charging.
Environmental Conditions
Temperature, battery state of charge, and charging speed all influence efficiency. For example, charging in extreme cold or heat may require additional energy for battery preconditioning.
What’s a Normal Charging Efficiency?
Different charging levels have different efficiency rates:
| Charging Type | Typical Efficiency |
|---|---|
| Level 1 (120V AC) | ~85-90% |
| Level 2 (240V AC) | ~88-94% |
| DC Fast Charging | ~90-99% |
Most home and public AC chargers operate at 85-94% efficiency, meaning 6-15% of the energy is lost. DC fast chargers tend to be more efficient but can still experience minor losses due to heat and cooling demands.
Want to learn more?
For more details, we recommend checking out these in-depth articles:
How Efficient Is Each Type of EV Charger?
Is your battery getting all the energy you pay for?
Additionally, you may find State of Charge, a YouTube channel dedicated to EV efficiency testing, helpful:
State of Charge YouTube Channel