The current go-to technology for EV battery packs is batteries based on lithium ion (Li-ion) chemistries. Li-ion batteries offer a lot of advantages including cost and energy density but one downside they have is, over time, their ability to hold a charge degrades.
While this is an inescapable characteristic of Li-ion batteries, there are things manufacturers can to do slow the rate of degradation. Tesla has invested significant R&D on cell chemistry and technologies to ensure your battery pack is coddled. While much of this happens behind the scenes, some visible examples include how the rate of charge tapers during Supercharging, how the heat or AC will automatically kick on to ensure your pack stays in its ideal operating temperature range and the 8-year battery warranty. In recent years, Tesla has added wording to the battery warranty to guarantee no more than 30% degradation.
Typically, owners see a drop of a few miles of rated range at around the one year mark, which can seem a bit disconcerting, but degradation is not linear. After the first big drop, pack capacity reduction seems to follow a much more gentle trajectory. Tesla recently released this chart of degradation across the Model S and Model X:
Considering these are Tesla’s oldest models with the oldest battery technology, it is a safe assumption that newer cars will see even better results–as Musk has stated, the goal is a million mile battery.
There are a few things you, as an owner, can do to improve pack health and slow degradation:
- The two biggest causes of accelerated battery degradation is spending too much time fully charged at 100% or at low single digit levels. It’s not a problem to charge 100% overnight if you are leaving on a trip the next morning, but try and minimize the amount of time you car sits around at either extreme.
- Related to that, try and avoid taking you car down to 0 miles of range. Hey, it happens and the battery pack as some protection mechanisms built in, but don’t make a habit out of it.
- Don’t needlessly range charge (i.e. over 90%) on consecutive days. In fact, if you do, the car will nudge you to lock down the charging level. That being said, if you need to range charge on consecutive days on occasion, it’s not the end of the world. My P85 is my daily driver and there are times I had trips on back-to-back days and I’d charge to 100% and the car would complain, but, hey life happens and both the car and I are still here to talk about it.
- Keep your car plugged in when you are not driving it. If it gets really hot or really cold outside (or in your garage) your car will wake up and heat or cool the pack as necessary to keep it in its happy operating range. The car will do this to protect the pack regardless of it is plugged in or not, but keeping it plugged in offers two benefits:
- The car uses “shore power” for heating/cooling, so you avoid running the risk of coming back to unexpected range loss
- The car will use battery power to heat/cool until the battery hits about 20% charge. If the car is plugged in, it will continue to heat/cool to protect the pack as long as environmental conditions dictate
- Keep you firmware up-to-date (this is a warranty requirement)
You will find there is no shortage of urban legends around coaxing the most out of your pack. My advice is to relax, enjoy your car and trust Elon and his engineers to do their jobs. If you ever have questions about the health of your battery pack, call Service and they can remotely take a look at your car and see if there is any case for concern. That being said, I am also a fan of having your own data and there are a number of apps and services available that will keep track of your battery’s operational characteristics and overall health and I think they are a worthwhile investment.