Why Does the Tesla Model S with a 40kWh Battery Accelerate Slower Than One with an 85kWh Battery?

Have you ever noticed that the Tesla Model S with a 40kWh battery seems to accelerate slower than its larger-capacity sibling, the 85kWh Model S? This isn't just a matter of personal preference—it’s a technical fact rooted in the physics of Li-ion battery technology. This article will delve into the reasons behind this phenomenon, analyzing the role of battery capacity, current draw, and how they affect the acceleration of these two versions of the popular electric vehicle.

Understanding Battery Capacity Limitations

The Tesla Model S, like many other electric vehicles, is powered by a high-capacity lithium-ion battery pack. The battery technology used in the Model S, however, has a fundamental limit: there is a limit to how much current you can draw from a single battery cell without damaging it. Simply put, the more cells you have in your battery pack, the more current you can draw without causing significant damage.

In the case of the Tesla Model S, the battery packs are composed of thousands of small, laptop-style cells. For the 85kWh version, there are over twice as many cells compared to the 40kWh pack. This design allows the 85kWh pack to provide a much higher total storage capacity and, importantly, more current capacity than the smaller 40kWh pack. This extra current capacity translates to better performance and acceleration, especially under high-power demands such as rapid take-off or sudden acceleration.

How Does Current Draw Impact Acceleration?

Electric vehicles, including the Tesla Model S, rely on the current drawn from their battery pack to generate power through their electric motors. As the vehicle's battery is depleted, especially during high-power usage, the available current becomes more limited. This limitation directly affects the performance of the vehicle, particularly in terms of acceleration.

The more current the battery can provide, the more quickly and efficiently the vehicle's electric motor can convert the electrical energy into mechanical energy. A higher current capacity means that the vehicle can draw more power more quickly, allowing for quicker acceleration. This is why the 85kWh Model S can achieve better acceleration performance compared to the 40kWh version.

The Physics Behind Battery Limitations

Despite the late hour, I can still provide a basic explanation of the physics behind these limitations. When a Tesla Model S is accelerating, the electric motor requires a significant amount of current. This current is drawn from the battery cells. Each cell has a maximum current rating, and when a sufficiently high current is drawn, the cell can be damaged, causing an increase in internal resistance and a decrease in overall efficiency.

The 40kWh version of the Tesla Model S, with fewer cells, has a lower total current capacity. Therefore, even though the vehicle has a smaller overall storage capacity, it is more vulnerable to the limitations of individual cells, leading to reduced performance during high-power events such as rapid acceleration. The 85kWh Model S, with its vastly increased number of cells, can maintain a more consistent current draw and, thus, better overall performance.

The Acceleration Performance Comparison

For the Tesla Model S, this means that during the later stages of charge depletion, the 40kWh version's acceleration slows down more noticeably compared to the 85kWh version. The larger pack in the 85kWh model can provide a more consistent and higher current draw, even as it is depleting, ensuring that the vehicle maintains better acceleration performance throughout its charge cycle.

Therefore, the observed difference in acceleration between the 40kWh and 85kWh Tesla Model S models can be attributed to the fundamental physical constraints of the battery technology used. The more cells a battery pack has, the more current it can provide, which directly impacts the vehicle's ability to accelerate efficiently and quickly.

When considering a purchase of a Tesla Model S, it is important to understand that the choice between the 40kWh and 85kWh versions should be based not only on range, but also on the intended use and driving habits. Drivers who plan to utilize the vehicle in frequent bursts of high-power driving, such as rapid acceleration, may find the 85kWh version more suitable and performant.