Journal of Energy Storage studies EV owner’s manuals, compiles best practices for batteries

Researchers at the University of Michigan this week published a paper titled, “Strategies to Limit Degradation and Maximize Li-ion Battery Service Lifetime.” The goal was to examine the best strategies for extending battery life, including for EV batteries. In the project, which was conducted in cooperation with the Responsible Battery Coalition, an industry association, researchers compared the owner’s manuals for electric cars with academic research.

While the findings are not surprising, they serve as a set of common-sense strategies for EV drivers, regardless of which car is owned.

Researchers looked for commonalities rather than specific technology employed by each maker (e.g., liquid versus air cooling).

Steve Christensen, executive director of the Responsible Battery Coalition, told Electrek:

The intent of the research was not to determine which OEM’s system works the best but to examine the guidance and best practices that can help prolong battery life. And hopefully, that will benefit everyone, including automakers and consumers.

What’s the number one most important recommendation for EV owners to avoid battery degradation? “Letting the battery discharge to 0% seems to have an incredibly negative impact on battery life, largely due to the additional stress this places on cathode materials,” said Christensen.

Following the recommendations spelled out in the owner’s manual could preserve range in an individual vehicle. But there are broad environmental implications as well. The paper states:

Battery degradation causes premature replacement or product retirement, resulting in environmental burdens from producing and processing new battery materials, as well as early end-of-life burdens.

Here are the eight recommendations that we summarized from the paper. We note which brand of vehicle provided the guidance in its owner’s manual.

• Every manufacturer includes a warning about high temperatures, though different strategies are suggested. Most companies do not cite a specific high temperature in which to avoid vehicle operation. Those that mention a specific temperature use either 50C/122F [Fiat-Chrysler] or 60C/140F [Tesla].
• Plug in the car anytime it’s hot, thereby allowing the battery cooling system to run as needed [Tesla and GM].
• Avoid parking in the sun on hot days [Kia].
  When the vehicle is plugged in, the BMS will measure the temperature and take the appropriate warming or cooling action before charging begins [Tesla, Ford, GM, Nissan, Honda], and may disable fast-charging capabilities [Kia]. The researchers advise: When the vehicle is running or charging, the BMS will regulate the temperature of the batteries, so it is most important to be aware of high battery temperatures when the vehicle is parked while not charging.
• Dealing with low temperatures is also cited by almost all EV owner’s manuals. Plugging in the vehicle when it is cold (below 0C / 32F) is recommended so that the battery heating system can run on grid power. The battery warmer will automatically activate below a specific temperature unless the battery is both not plugged in and under 15% charge (to avoid over-discharge) [Nissan].
• Extremely low temperatures for extended periods may cause irreversible damage, necessitating battery replacement [Mercedes-Benz]. The lower temperature limit for batteries is cited as −25C/ -13F [Nissan, Mercedes-Benz] or −30C / -22F [Tesla, Honda].
• Over-discharging will typically not occur during operation. The BMS will turn off the car and cease operation before severe degradation occurs. However, if the “empty” battery is then left for an extended time without being recharged, the battery can enter an over-discharge state due to the slow self-discharge that occurs even when the battery is not operating. Some manufacturers are concrete, instructing owners not to leave the vehicle parked for more than two weeks with a low battery (20% state of charge) [Tesla, Mercedes-Benz].
• If possible, don’t allow the battery to be run all the way down, or left idle for extended periods [BMW, Hyundai, Kia, and Honda].
• The majority of manufacturers do not include information in their manuals explaining that fast charging can lead to accelerated battery degradation. Those that say use of fast chargers should be minimized to maintain battery life [Ford, Nissan, Kia, Honda].

From the dashboard of a 2019 Nissan Leaf. Gary Lieber, who took the photo, added the text to describe the graphic’s meaning.

As you can see, temperature is a significant factor. But does that mean people living in very hot or cold climates should not drive an EV?

“Absolutely not,” said Christensen. “If anything, this research further supports the need for responsible battery management in those more extreme temperatures. The research also shows how the guidance from OEMs helps consumers best manage their batteries in both hot and cold climates.”

What steps do you take to preserve the life of your EV’s battery?