Battery Range Performance
Many Tesla owners are interested in the change in the max capacity of their battery over time. While some refer to this as 'Battery Health', in order to be more precise, we refer to this as 'Battery Range Performance' (see our note on this below). The Battery Range Performance measure in TezLab is an extrapolated estimate of the maximum range of your fully-charged battery. TezLab will calculate this value on select charges and keep track of it over time.
The range trend should be considered over the long term as there will be variation between individual charges. In order to get the most accurate extrapolation possible, we only estimate battery capacity on charging sessions where a significant amount of energy has been added to the battery (we recommend at least 30%) and where the ending state of charge is 90% or greater. This also ensures that a long-term trend is plotted rather than short-term, normal fluctuations.
It is important to understand that this trend is produced by data points reported by your vehicle's software, and is in no way intended to be a representation of the physical condition of the battery pack.
What do I do about a downward trend?
If you notice a downward trend over time, especially if you typically do short drives and charge your battery almost daily (i.e. you keep it between 50% - 80% most of the time), community experience suggests that this is likely a difference in Battery Management System readings rather than true degradation. The Tesla community has shared some unofficial but often effective methods of resetting things.
Note that this should only be attempted periodically, as generally, the battery should not be below 20% for an extended period of time, nor should it regularly be charged to 100%.
A note on the term "Battery Health"
Previously, we described a chart in TezLab as "Battery Health". While the information tooltip has always been clear about the source of this data, we now refer to this as "Battery Range Performance".
No app can accurately describe your battery health. If any app suggests otherwise without a disclaimer, they are incorrect. The information reported by Tesla vehicles does not contain any metrics that can accurately determine the chemical health of the battery pack in your vehicle. In all cases, readings are based on the range values reported by the vehicle's software which vary significantly due to several factors, many of which are unknown.