by Morris Kesler, CTO, and Oguz Atasoy, Senior Staff Scientist, WiTricity
Based on the popularity of our 80% Rule blog post, it’s obvious there’s a lot of interest in increasing an electric vehicle’s battery life. So here are two additional tips for charging that can have a direct impact on your battery’s lifetime.
Using a Derating Approach Can Extend the Life of Your EV Battery
Derating? What’s that? Let’s start with a couple definitions.
State of charge (SOC) is the ratio of the energy in the battery relative to the maximum energy that the battery can hold. A fully charged battery has 100% SOC, while a totally empty battery has 0% SOC. Generally, EVs have battery management systems that prevent these extremes.
Derating? It’s the operation of a device at less than its maximum capability in order to ensure safety, reduce degradation, and avoid system shutdown.
The battery in your EV is one of the most expensive components of the car, so protecting it is critical. Derating is one approach for extending the life of the battery. Better still, derating can be implemented easily and has no impact on system reliability.
It’s time to rethink your charging behavior and forget the gas station model you grew up with. Most people driving an ICE vehicle wait until the gas tank gets low and then fills it up to the top. This brings us to …
Rule #1: Don’t completely deplete your battery and minimize 100% SOC. Electric cars already have an installed battery management system that prevents the battery from being charged and discharged at the extremes of SOC, and every EV manufacturer has charging recommendations for their individual models. So, in general, don’t regularly charge to more than 90% or drop below 10%. Yes, it’s ok to charge to 100% (if the car will allow it) for a long trip, but the optimum charging range for maintaining battery integrity in most electric vehicles is 25-75%. It will improve the overall lifespan of your battery.
Rule #2: Fast is not your friend. Don’t rely on fast charging to meet your day-to-day charging needs. Unless you’re going long distances, it’s important to use a Level 2 (or equivalent) charger for daily charging. Fast charging puts more stress on a battery and reduces battery life and, as a result, the battery will drain faster.
It’s hard to break old habits but, with an electric vehicle, you have an opportunity to create new habits that will prolong the life of your vehicle. To explore more about EV charging, check out this blog post.
Battery derating will become easier when there is pervasive wireless charging. Then, wherever you go or wherever you park, you can get a little Power Snack™ so you’ll always have sufficient battery power, Goldilocks style. Not too much, not too little, just right.