Battery degradation is one of the biggest concerns for electric car owners and potential buyers, but data from Tesla battery packs have been very reassuring so far.
Now the latest data shows less than 10% degradation of the energy capacity after over 160,000 miles on Tesla’s battery packs.
A group of Tesla owners on the Dutch-Belgium Tesla Forum are gathering data from over 350 Tesla vehicles across the world and frequently updating it in a public Google file.
We have previously reported on the data, but they have since added many more vehicles and those vehicles have been driving a lot more – completing more battery cycles.
The data clearly shows that for the first 50,000 miles (100,000 km), most Tesla battery packs will lose about 5% of their capacity, but after the 50,000-mile mark, the capacity levels off and it looks like it could be difficult to make a pack degrade by another 5%.
The trend line currently suggests that the average battery pack could cycle through over 300,000 km (186,000) before coming close to 90% capacity.
Here are the relevant charts from the data gathering effort (full chart on the left and zoomed to 80% on the right):
There are a few outlier battery packs out there and they tried to figure out why by gathering other data, like frequency of DC fast-charging and daily state of charge, but there’s no clear indication that any of those factors have any significant impact based on their data.
With this said, Jeff Dahn, a renowned battery researcher and the leader of Tesla’s research partnership through his battery-research group at Dalhousie University, said that he recommends charging to only 70% daily in order to extend battery life.
Tesla warns that it does not cover battery degradation from “battery usage” under its Model S and Model X warranty up to any specific level:
“The Battery, like all lithium-ion batteries, will experience gradual energy or power loss with time and use. Loss of Battery energy or power over time or due to or resulting from Battery usage, is NOT covered under this Battery Limited Warranty. See your owner documentation for important information on how to maximize the life and capacity of the Battery.”
But for the Model 3, Tesla introduced a warranty with a new 70% battery capacity retention guarantee.
The Model 3 is equipped with different battery cells and a new battery pack architecture, but if data from the Model S is any indication, it shouldn’t be an issue.