The time on the screen is a live forecast, not a promise. Your car works it out by dividing the energy the battery still needs by the charging rate at that moment, and it repeats the sum whenever the rate changes. Because charging speed rises and falls during a session, the finishing time moves with it.
Key Takeaways
- The time shown is energy still needed divided by the current rate, recalculated live.
- The taper near full, battery temperature and shared power move the rate, and the estimate follows.
- Trust the percentage for planning; the clock is a forecast that settles as the session runs.
- A rate stuck near zero is a fault to check, not a forecast.
How the Estimate Is Worked Out
The maths is simple: time remaining is roughly the energy still to add, in kWh, divided by the current rate, in kW. Add 20 kWh at a steady 10 kW and the car shows about two hours. The weak point is the word “steady”. The estimate assumes the rate on screen right now will hold until the end, and it usually does not. Each time the rate shifts, the car quietly recalculates and the clock changes. The U.S. Department of Transportation’s guide to charger types and speeds shows why rates vary so much: Level 2 charging alone spans 7 to 19 kW.
Why the Charging Rate Moves
Most movement in the estimate traces back to the rate. These are the usual causes:
| What changes | Effect on the rate | Effect on the estimate |
|---|---|---|
| Battery fills up | Rate tapers down, especially past about 80% | Time remaining grows |
| Battery warms up | A cold battery accepts power slowly, then faster | Time remaining shrinks |
| Power is shared | Load management or a second car takes a share | Time remaining grows |
| Cabin heating runs | Part of the incoming power feeds the heater | Time remaining grows |
The taper near full is the biggest factor on most sessions; we explain it in why EV charging slows down after 80%. Temperature works the other way at the start: a cold battery charges slowly, then speeds up as it warms, which is why an estimate given in the first minutes is often pessimistic. Battery preconditioning exists to warm the pack before charging for exactly this reason.
The Target Moves Too
Sometimes the rate is steady and the goalposts move instead. If you raise or lower the charge limit mid-session, the car has a new amount of energy to add and re-times the session at once. The car also refines its own reading of the battery as it measures voltage during charging, so the percentage itself can be adjusted slightly, and the estimate follows. Finally, if you start heating the cabin or the battery while plugged in, some incoming energy is diverted, and the finish time stretches even though the charger is delivering full power.
How Much Should You Trust It?
Treat the estimate as a forecast that improves as the session goes on. The first figure, based on the first minutes, is the roughest; by the second half it is usually close. For planning, the percentage is more dependable than the clock: a target of 80% by morning works even if the predicted finish time wanders. A sudden collapse is different. If the rate falls close to zero and stays there, or the car shows an error, that is a fault, not a forecast, and it is worth checking the connection and the charger, or contacting the manufacturer.
An app-connected wallbox makes the moving numbers easier to read. The EVDANCE EV-ACT3204PE 22 kW wallbox offers RFID and app control, so you can watch the live rate and session energy and see for yourself why the car’s finishing time changed.
Frequently Asked Questions
Why did my car say two hours, then four hours?
Because the rate fell after the first estimate. The usual cause is the taper as the battery fills, a shared circuit giving power to something else, or power being diverted to heating. The car re-times the session at the new rate.
Is a changing estimate a sign of a fault?
Almost never. It is the car recalculating with fresh numbers. Worry only if the rate drops to near zero and stays there, or an error message appears.
Why is the estimate more accurate near the end?
Less of the session is left to guess. Early on, the car cannot know how the rate will taper or how the battery temperature will change; near the end, most of those unknowns have already happened.
Related Reading
- Why Does EV Charging Slow Down After 80%?
- How Many kWh Does It Take to Charge an EV?
- What Is EV Battery Preconditioning?
- Smart Charging and Time-of-Use Tariffs: How Scheduling Cuts EV Charging Costs
