Battery Best Practices

When I got my first EV (2017 Nissan Leaf), I gathered from various sources there were things you should do and things you should avoid to extend your car’s battery life. Batteries make up about 35% of the cost of an EV, so you want to make them last. However, the owner’s manual was light on advice and the internet was full of conflicting information about what was important.

An EV-savvy friend told me the simplest rule was to keep your battery between 10% and 90%, and don’t let it sit at 100% charge for long time periods. When you fill it to the top, start drawing it down soon. That is good advice, but I like to know WHY a thing is important and WHO says so.

Finally, University of Michigan researchers have studied the issue and came up with some easy to understand best practices. Why should we care about treating our EV batteries right?

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.

Center for Sustainable Systems, School for Environment and Sustainability, University of Michigan researchers

Below are eight best practices as summarized by the Electrek.co article cited in the quote below. Follow the link to the article to learn more about the study.

Here are the 8 recommendations that we summarized from the paper. We note which brand of vehicle provided the guidance in its owner’s manual.

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

• 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 Most companies do not cite a specific high temperature in which to avoid vehicle operation.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 50° C / 122° F [Fiat-Chrysler] or 60 °C / 140° F [Tesla].
• Plug in the car anytime it is 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 (battery management system) 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 0° C / 32° F) 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 −25° C / -13° F [Nissan, Mercedes-Benz] or −30° C / -22° F [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 2 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].