How to check battery health

What health means

Battery health is usually given as the share of its original energy a battery can still hold. It is not the range on your screen, which is a calculation from the energy left and a consumption figure, and it cannot be read from a single charge.

Tesla's own battery health test

Tesla's owner's manual describes a Battery Health page under Controls, then Service. It shows an evaluation built from the battery management system's data, compared with the retention expected for a battery of that type, age and usage. Tesla notes that not every car has it and that it needs a Wi-Fi or cellular connection.

The same page describes a full Battery Health Test. Tesla's requirements: an AC charger of at least 5 kW, the car in Park, no battery-management alerts, no pending software update, and the battery below 20%. The test can take up to 24 hours. It drains the battery below 10%, possibly to empty, with Sentry Mode and climate off, then reports how much energy the battery retains compared with new, and may recalibrate the range estimate.

It cannot be run again until the battery management system detects a measurable change, and Tesla advises running it only if you are concerned. That makes it the most direct measurement an owner can get, and a demanding one: a day without the car, a nearly empty battery, and one result rather than a trend.

What the range figure can tell you

Tesla's manual says the range shown in the car is an estimate based on rated consumption, not on how you drive, so it can fall faster than the distance you cover; the Energy app offers a projection from your recent consumption instead. Tesla also says range may dip slightly in the first months and then level off, with gradual decline after that, and its support pages note that cold weather raises energy use.

A common home method is to divide the range shown by the state of charge, so 300 km at 75% implies 400 km at 100%, and to watch that figure over months. It makes a reasonable trend line, but it moves with temperature and with the car's own recalibration, and it is coarse at low charge. Compare readings taken at a similar charge level in similar weather, and never conclude anything from one reading.

Reading the numbers together

No single figure settles it. Tesla's test is one precise point in time; the range ratio is a noisy trend; a capacity estimate from charging needs several long sessions before it means anything. When they agree, you can trust the picture. When they disagree, look at the conditions first, such as temperature, a recent recalibration or a run of short charges, and wait for more readings before concluding that the battery itself has changed.

Tesla's manual also has its own list of tips for looking after the high-voltage battery, and one of them is simple: keep the car plugged in when you are not using it.

The warranty line

Tesla's US warranty page covers the battery for 8 years, with at least 70% of its capacity retained over that period, and a mileage limit of 100,000 or 120,000 miles depending on the model and version. Tesla points out that the warranty supplied with your car is the one that applies, and that you can read yours in the Tesla app under Specs & Warranty. Outside the US, check your own warranty rather than this summary.

How DashM8 does it

DashM8 shows two numbers side by side. The first is Tesla's own state of health, read once from your car's specifications when you connect and shown with its date, because it is a single measurement rather than a trend. The second is our estimate from the stream: hourly rated range divided by state of charge over the past year, ignoring readings below 20%, with the recent median compared with the year's best; plus a capacity estimate from charging sessions that added at least 20 percentage points.

When both exist, Tesla's figure is the calibration point and our estimate shows how far the battery has moved since Tesla measured it. Each figure carries its confidence, and with too little data the app says so instead of printing a number; it needs a few weeks of driving before it says anything. Battery health with Tesla's own figure is part of the free plan.

Sources

Every source below was checked on 7 October 2026. Prices, tariffs and Tesla's pages change; check the source before you rely on a figure.

1. Tesla Model 3 Owner's Manual: Battery Health
2. Tesla Model 3 Owner's Manual: Getting Maximum Range
3. Tesla Support: Range
4. Tesla Support: Vehicle Warranty
5. Tesla: Model 3 Owner's Manual (PDF)