DIMO Insights #3 - How EV battery health scoring could save your car's battery

DIMO Insights went deep on electric vehicle batteries and found the most important factors that impact their health and value over time. 

1. Similar to the battery in your cell phone, the battery in an electric vehicle is happy when it’s between 20% and 80% charged. 

2. Frequent charging on level 3 chargers degrade the life of the battery over a long term period.

3. Generally the battery will last longer if the average depth of discharge is lower. Discharging your battery fully from 100%→ 1% and back to 100% is harmful.

How can DIMO use car data to calculate a Battery Health Score?

Using data from level 3 charging, undercharging,  to build a score of how well a driver is taking care of their electric vehicle battery. In the future, we will add insight into the expected lifetime of the battery by counting charging cycles and mileage.

By assigning weights to these metrics based on their importance, we're able to construct a 100 point scale to determine an EV battery's health.

Level 3 charging frequency = 20% weight

Time in undercharged range = 20% weight

Time in overcharged range = 30% weight

Average Depth of Discharge = 30% weight

Breaking down DIMO data from a test driver

This driver keeps their battery in the “Happy Battery Zone” for about 70% of their driving. They are undercharged 14.15% of driving and overcharged 15.51% of driving. They also frequently use a level 3 (aka supercharger), for about 86.22% of their total charging, which lowered the Battery Health Score immensely.

Using DIMO data to visualize battery health

As a result of this charging and driving behavior, this driver’s battery health score would be 49.63%, mostly based on the fast charging and the high average depth of discharge. For comparison, the average depth of discharge is 50.4%, the average amount of level 3 charging is 24.7%, and average battery health score is 74%.

With DIMO visualizations, this driver is able to see the full breakdown of why their score is so low, and learn what they can do to improve it.

Battery Scores predict degradation and lifespan of your EV battery

Battery degradation is extremely hard to predict and analyze as it is dependent on a multitude of factors. These include weather, level of aggressive driving style, charger type used, charging frequency, etc. While calculating battery scores won’t allow users to know exactly how much their battery is degrading, it can help predict degradation trends and inform EV drivers how to better treat their batteries to ensure minimal degradation.

Battery health metrics could make or break the value of an EV on the market.

The batteries are the most expensive component of an electric vehicle. So where a vehicle may show 50k miles on the odometer, that will not take into consideration how the battery has been treated in that time. A battery in a vehicle charged from level 1 or 2 chargers and kept between 20% and 80% state of charge will have a longer usable life than batteries treated differently.

As with gas engines, batteries will experience some degradation regardless of driver behavior, but the bottom line is this: how your battery is treated affects the vehicle’s life and under normal operating conditions you can get hundreds of thousands of miles without issues.

Fast charging can be detected based on the vehicle data collected. The specific impact of charging with a level 3 charger will vary by vehicle (e.g. battery size, weather, etc.) but overall level 3 charging decreases the life of a battery when compared to level two or level one charging.

We can use the percentage of driving taking place outside the “happy battery zone” and the percentage of charging that takes place at level 3 chargers to grade how DIMO users are treating their batteries.

Interesting findings from DIMO user battery scores

• There are some heavy supercharger users: 5% of drivers (53 out of 1,145) charge more than 90% of their miles added from level three chargers.

• Not surprisingly, these drivers typically have low scores: The 141 vehicles with scores under 65% add an average of 79.83% of their miles from level three charges and have an average depth of discharge of about 61.91% (while they drive undercharged for only about 6.78% of their miles and overcharged for about 13.77% of their miles).

• Scores are more impacted by supercharging and average depth of discharge vs undercharged or overcharged.

• Top scoring batteries are rarely supercharged: The 161 vehicles with the highest scores (over 82%) have an average of 2.76% of their miles added from supercharging and the global average for miles added from supercharging is about 24.71%. Further, these vehicles with the highest scores have an average depth of discharge of about 39.63%, where the global average is 50.42%.

Over time we plan to integrate more variables - things like climate around the vehicle and software updates can provide a more accurate picture of battery health and vehicle valuation can be given to DIMO users. 

Further Reading

The DIMO Insights team has also explored scoring ICE vehicle drivers for compatibility with electric vehicles, and an expected amount of their normal driving behavior would be satisfied by only level one or level two charging only at home. Drivers could get an estimate of how much level three charging might be necessary with their driving patterns in advance of an electric vehicle purchase.

• Between January 19, 2022 and November 4, 2022, DIMO connected Teslas have charged for a combined 86 years

• These drivers have driven farthest on level 2 charging, yet spent the most amount of time charging on level 1.