Something to bear in mind about electric cars is that their batteries will degrade slightly over time. As the batteries age, the maximum range obtainable from the batteries on a full charge will go down. How quickly this happens will depend on how you use and how you charge your car, and in this blog post, I’m going to talk about the impact of charging to 100% on your battery’s health.
In our previous diesel car, we would usually let the fuel tank run down until it was in the red zone (about 1/8 full) and then fill it up. The exceptions would be when we’re about to go on a long journey, and so we would fill up before departing to save having to stop off on the way.
With our electric car, we follow the advice of generally keeping the charge level between 20% and 80%. A quick web search finds several different articles backing this up. But we do also charge to 100% sometimes:
When you should charge to 100%
If you’re about to go on a journey where you need the range, then charging up to 100% makes sense. This is especially so if you’re charging at home, as this will be much cheaper than paying to do so at a public charger. There’s no point in only charging to 80%, if this would mean that you have to stop and charge on your journey, when a 100% charge would allow you to complete your journey without a break.
Occasional charges to 100% are probably not going to contribute significantly to your battery’s degradation.
When you shouldn’t charge to 100%
The batteries in your car tend to work best at between 20% and 80% charge. Going outside this range can stress the battery, and doing so regularly may result in them degrading faster. This is also why rapid public chargers slow down the rate of charge after your battery reaches 80%.
Therefore, if you’re not planning a long journey, then it’s best to stop charging your car at around 80%. It’s also worth noting that some cars will limit the effects of regenerative braking above 80% charge, so your driving will be less efficient until your battery drops below 80% charge. Route planning apps should estimate how much charge you will need for your journey, and whether it’s worth charging to 100%.
Also, if you’re using a public charger and don’t need a full charge, then it’s courteous to stop charging at 80% and move your car to a non-charging bay, so that someone else can use it.
Is battery degradation a big problem?
Battery degradation is something that owners of electric cars should be somewhat aware of, but I also think that it’s less of an issue than some make it out to be. We didn’t buy our Nissan Leaf new – it was three and a half years old, and with around 33,000 miles on the clock. Its battery capacity isn’t quite as much as it would have been fresh from the factory, but we’re talking about a reduction of maybe four miles, which is less than 2%. If you extrapolate that, then by the time the car is around 10 years old, the battery degradation may reach 5-6%. But that still means that the battery can hold almost as much charge as new.
Obviously, we’ll do what we can to try and preserve the battery’s capacity for as long as possible, although there will be the occasional 100% charge when necessary.
