Why does the remaining-range estimate change so much in my electric car?

Not necessarily. Treat the displayed range as an estimate, not a distance guarantee. For a Tesla Model 3, the manual says the displayed estimate is based on EPA-rated consumption and may not reflect personal driving patterns or external conditions; it can fall faster than the distance driven. The manual also describes an Energy app estimate based on recent energy consumption. [S1]

Those explanations are specific to Model 3. For another make or model, check its owner’s manual for how its estimate is calculated. A changing estimate alone does not establish a fault, and the supplied information does not provide a way to diagnose one.

Keep a short record without trying to drain the battery. For each ordinary trip, note the starting and ending displayed range, distance driven, and the vehicle’s energy-consumption reading if it provides one. Also record the route and brief notes about driving habits or conditions that might help you compare like with like.

For Model 3, its manual says average consumption varies with route, habits, and environment. Its Energy app can compare actual consumption with rated consumption over selectable distances; a longer interval includes more driving behavior and environmental variation. [S2] A comparison over several normal trips is therefore more informative than treating one changing number as a test. The source does not establish a universal logging period or a fault threshold.

Use this copyable template. The example is hypothetical; replace it with your own readings.

Range observation log

• Vehicle/model: [make, model, year]
• Date or trip label: [date / Trip A]
• Start displayed range: [number and unit]
• End displayed range: [number and unit]
• Distance driven: [number and unit]
• Energy reading, if available: [value, unit, and screen/app]
• Route: [brief description]
• Driving notes: [brief, factual notes]
• Conditions or other context: [brief notes]
• Compared with: [another trip or selected interval]

Hypothetical example: “Trip A; start 180 mi; end 151 mi; distance 22 mi; energy reading: [not recorded]; route: [mostly familiar commute]; notes: [ordinary drive].” This example illustrates how to fill in fields; it is not evidence about expected range or vehicle condition. Keep units consistent and leave unknown fields blank rather than guessing.

Use it as another view of consumption, not as a guarantee of future distance. The Model 3 manual describes real-time and projected energy views and a comparison of actual with rated consumption over selectable distances. It notes that longer intervals include more variation from driving behavior and environment. [S2]

Choose an interval that helps answer your question, then write down which interval you used so you can compare the same view later. If you switch interval lengths, record that too; otherwise, two app readings may not be directly comparable. The manual excerpt does not establish that an app estimate predicts a particular trip outcome, nor does it supply a universal threshold for when to seek service.

Keep the log and consult the owner’s manual for your exact vehicle. If you contact a qualified service provider, share your recorded readings, units, routes, and any messages displayed. Ask how your model calculates its range estimate and what information they need to assess the concern.

Avoid deliberately driving until the battery is nearly depleted as a test. Your log can help describe what you observed, but it cannot by itself determine whether a vehicle has a fault.