Batteries lose capacity over time. The process can be slowed down, but it’s inevitable, so after a few years, your EV won’t provide quite as much range as when it was new. The battery will lose about 12% of its capacity in a Tesla due to degradation after 200,000 miles.

For the Model 3, for instance, Tesla says that up to 30% degradation is normal after 8 years or 120,000 miles driven. Interestingly, many owners who like to keep track of their car’s battery degradation note that the first 5% of capacity vanishes quite quickly, sometimes within the first year and a half, depending on how the vehicle is used. However, it takes much longer for the battery to lose another 5%, at least in a non-LFP-equipped Tesla.

To calculate how much capacity a Tesla has lost, you have to find out how much energy its battery can still store and then compare that to the battery’s official quoted capacity. The only problem is that Tesla is one of the few manufacturers that doesn’t list the exact number of kilowatt hours for its vehicles, so you must find alternative sources that list the capacity.

When trying to find the capacity of a given Tesla battery pack, it’s worth noting that some sources list the gross or total capacity, which includes the buffer. In contrast, others only list the usable capacity, which is smaller and doesn’t include the buffer. For instance, the new 2024 Tesla Model 3 Long Range Dual Motor battery has a gross capacity of 78.1 kWh and a net capacity of 75 kWh, which means it has a 3.1 kWh buffer.

So, how do you calculate battery degradation in your Tesla? The simplest way would be to charge it a set percentage (80% or 100%) and compare the range estimate to what it offered when new (assuming you kept track of that). However, this will just give you a rough idea of how much capacity it still has, and there are ways to get a more accurate result.

You can more accurately calculate degradation using figures from the vehicle’s energy screen. It shows a graph of the vehicle’s energy consumption and its projected range. You can use these two figures plus the battery state of charge percentage displayed in the top right corner of the screen to check how much current the battery still holds—this saves you from having to charge to 100% when you want to do this calculation.

You multiply the average electricity consumption, which by default is displayed in watt-hours per mile, by the projected range, and you should get the number of kilowatt-hours currently in the battery. Then you convert the battery percentage into a decimal— 80% becomes 0.8—and then you divide your resulting kilowatt-hours by this decimal to get a pretty good idea of how many kilowatt-hours your battery could theoretically hold when fully charged.

There are also apps like TeslaFi that track your vehicle’s charging stats, and you can see how the vehicle’s range is affected by degradation over time. You can even check out the TeslaFi portal, where you can see results from app users and see what kind of range difference they observed—it shows the first and last charging sessions that went over 80% and the predicted range for each.

You can also check the battery capacity on your Tesla’s main screen by putting the vehicle into Service Mode. To access it, you tap on the car icon in the lower-left corner of the screen, then go to Software. Hold down on the model badge on the screen until a password prompt comes up, where you enter the word “service.” This will enable the service mode.

The vehicle recommends that only Tesla personnel should perform this action and that it should be done while the vehicle is stationary. However, you can also do it yourself without affecting the car, and it’s the best way to check the level of battery degradation. So once in Service Mode, you will tap on the Battery menu, then High Voltage and then be able to perform a battery health test.

If this test has never been performed on your Tesla, the first time you access this screen, it will say the battery health is 100%, even if your vehicle is a few years old, and it’s no longer true. To start the test, you must follow three commands involving the indicator stalk in Teslas that still have one, then press the brake pedal and place the key card where the car can read it.

To get a result that reflects your vehicle’s current battery health, you tap on the Health Test button, and it will bring up a prompt to alert you that this test requires the state of charge to be below 50% and the vehicle needs to be plugged into a Level 2 charger. It also says the test may take up to 24 hours to complete, during which time the battery will be completely discharged and then fully charged—this is the only way to get an accurate reading of the actual usable capacity.

You know the test has started when the battery cooling fans turn on, and they will stay on high until the vehicle's battery fully drains. Then you get out of the vehicle and leave it to do its test until the next day when it will produce a percentage to tell you how much of its original capacity it still has.