Battery Life of an EV

There is quite a bit of academic research on battery degradation, especially for Lithium Ion batteries used in electric vehicles. We went through a few of the papers which discussed what factors effect the life of an electric vehicle’s battery and developed a working model for battery degradation.

According to Review and Performance Comparison of Mechanical-Chemical Degradation Models for Lithium-Ion Batteries, there are various ways that Lithium-Ion batteries degrade, such as lithium plating, surface cracking, and pore clogging to name a few.

One of the key parameters that determines the battery life, is temperature, and in the article mentioned above, they modeled three heat sources that effect the battery:

  • Heating due to DC resistance fo the battery Rbatt
  • Reaction heating due to the overpotentials
  • Entropic heating listed as (∂OCV )/( ∂T)

〖pvc〗_p  ∂T/∂t  =I^2  R_batt  + I (n_neg-n_pos )+ IT (∂OCV )/( ∂T)  - hA_batt  (T - Tenv )

Without going into the details of the model, the point the authors were making is that there are multiple sources of heat which degrade the battery.

For car owners, fleet managers, what this means is that supercharging/DC charging, high current charging, as well as extreme high/extreme low temperature will reduce the battery life.

Real-World Tesla Battery Data

With over 20m miles of aggregate data, we looked at how battery range is impacted by the items mentioned in academic papers, and based on feedback from Tesla as well.

“Do not over-use Supercharging”

As high direct current charging does have an impact on temperature, excessive use of supercharging, especially in warm climates does have an adverse effect on battery life. In our modeling, we had data for both Level 1, Level 2 and supercharging, and we built our model looking at all these in aggregate.

“Charge 95% and below for your SoC”

Although Elon has stated that newer models can have 99% State-of-Charge (SoC), it is inconclusive for our models since these vehicles are relatively new. We have looked at vehicles charging at 100% SoC continuously and have seen a drastic impact on battery life.

Some Tesla Models from 2018-2020 charged at 100% and their batteries dropped to 67% battery life in a matter of months.

Location Matters

We noticed hot temperature areas have a lower battery life than those in cooler climates. A Tesla in Phoenix have a lower battery life than the same Tesla is Seattle for example. Likewise if a vehicle is in continuous cold climate, it will have a poor battery life, but that situation is rare, as there are more areas of excessive hot temperature for longer term than colder temperatures.

Age / Odometer Matters

As a battery ages, there is some decay associated with time, but unlike ICE vehicles, odometer is not the most telling factor in the condition of an electric vehicle. A high mileage / old age EV can still function relatively well (with respect to its battery and range) than a similar mileage ICE vehicle.

In our fleet of vehicles, we have high mileage Teslas that have excess of 200,000 km (125,000 mi) and are in better shape than lower mileage models which have had a poor charging history.

The Keemut Battery Degradatino Model

You can see how battery life of a Tesla is effected by changing parameters, and if you have a Tesla, you can connect it with the Keemut platform and start to track your battery health automatically.