By Keith Beckley
When contemplating the move to an electric car, consumers typically have questions about the differences between a gas-powered car and an electric car. Questions such as “How far can it go?, Where will I charge it?” and “Will it save me money?” are common. Those questions all have good answers but there are two other very common questions: “How long will my battery last and how much will it cost to replace?”
These questions can be answered simply as: “For the life of the car, so zero dollars! This answer may surprise many, but real-world evidence says that it is true. This article will explain why the battery will outlast the car.
For most of us our experience with batteries consists of use and throw away batteries and rechargeable batteries that start off great then fade to being useless. Our expectation is that rechargeable batteries will eventually lose their capacity to charge.
The main reason for this expectation is our everyday experience with rechargeable batteries in smart phones and laptop computers. Batteries used in these devices all use lithium ion chemistry. Lithium ion chemistry far and away has the best performance: the most energy stored per kilogram and most energy stored per liter of volume. This is exactly what cell phone makers and computer makers want because you want your phone to be lightweight and your laptop to last forever when unplugged. So, if our phones stop lasting all day after a few years will cars not be any different and have almost no range since they also use lithium ion chemistry? The answer is no and that is because the reasons for why rechargeable batteries degrade is well understood. The secret to NOT having lithium ion batteries lose charge capacity is twofold:
1. Don’t leave them charged at 100%.
2. Do not let them get hot (especially if they are charged at 100%).
Laptop manufacturers want to give you the best performance, so they put in the best processors that run higher temperatures. Same for cell phones. Over time your battery degrades. While you can replace your phone battery (or get a new phone) this is not an option for cars when the cost of a new battery will be greater than $15,000.
So how do electric car companies avoid the degradation trap? Simply, they show the batteries great love. Foremost, the batteries get a dedicated cooling system that keeps them at a safe low temperature. Famously, electric cars do not have radiators in the front as there is no engine (running at ~25% efficiency) to cool. But look carefully and you will find a small radiator used to keep the battery pack cool. In fact if it is really hot out (driving through the desert at noon) the pack will use some of its own energy to run a small cooler to keep the temperature down.
Also manufactures “cheat” on what a 100% charge means. Your display might say 100% but the manufacturer has really only charged the pack to, say 96%, thereby ensuring that the pack again is kept safe (they sacrifice some initial range). Obviously cell phone manufactures have no room for coolers and they allow the battery to go to 100% since how long the battery lasts (on the day you bought it) is a key specification on which consumers base their purchasing decision.
There is another reason a car battery will last longer and that is because not all lithium ion batteries have the same chemistry inside. Lithium ion batteries are named after the element because the small lithium atom is the one that moves back and forth between the anode (+) and cathode (-) to allow the electricity to flow. In fact lithium only makes up about 3% of the weight of the battery. The rest is made up of nickel, graphite, cobalt, aluminum and some secret chemicals in the electrolyte (material between the anode and cathode). This electrolyte can be optimized for longer life or higher energy density but not both.
Cell phone manufactures opt for energy density while electric car manufactures opt for longer life (charge cycles).
So, if kept at a nice temperature and not left at a true 100% charge how long will an electric car battery last? Tesla is considered to have the best battery chemistry for car batteries and there are a few 6-year-old Teslas that have well over 300,000 km on their odometer and still charge to over 90% of their original range. My personal Model S that I purchased in 2012 charged to 410 km at 100% full charge. Today, with 192,000 km driven a full charge range is 380 km. That is a remarkable 7% degradation over 6 years.
Most of that degradation actually happens in the first year, after that it is very slow. My battery technology is now 6 years old. In this rapidly changing technology, the batteries I could buy today are significantly better than mine. Tesla believes their current batteries will easily last for over 600,000 km and within a few years they will last for 1.5 million km.
No car lasts that long – very few people ever drive that far. Think if your car has gone 400,000 km and you still have more that 90% of your original range available with a full charge. If the battery originally had a capacity of 80kW so it now has a capacity of 72kW. 72kW will run your house for 2 days! Suddenly that old battery looks very valuable and someone will pay you for it.
Buying an electric car requires the consumer to educate themselves about the technology. Fear of having to replace a battery is one item that can safely be put into the “not a worry” bucket.