A charging receipt and a trip computer can describe energy at different boundaries. Before deciding that either number is wrong, identify where it is measured, what it includes and which period it covers.
The U.S. Department of Energy and EPA explain that energy is lost during charging, including AC-to-DC conversion and battery charging. Their published efficiency diagrams use particular test cycles; they do not establish one loss percentage for every car and household.
Put the receipt period and the trip display’s reset point on the same worksheet. Then label what each figure measures. Aligning the period and measurement boundary gives the comparison a clear basis and helps identify which additional information would explain a remaining difference.
Draw the path before comparing totals
Start with electricity supplied, then distinguish energy stored and energy used during driving. Check the manufacturer’s definition of the trip figure, including its stated treatment of parked or connected use.
Also compare beginning and ending charge levels. If the battery ends the week with more stored energy than it began with, the week’s charging and driving figures are not expected to describe the same net energy movement.
Reconcile a hypothetical log
| Recorded quantity | Invented example |
|---|---|
| Electricity recorded at charging boundary | 60 kWh |
| Energy recorded for driving | 45 kWh |
| Difference to investigate | 15 kWh |
The difference is not automatically a charging-loss measurement. You would still need matched dates, consistent boundaries, the change in stored energy and any other included or excluded uses. These numbers are a demonstration, not a vehicle test.
Use the right total for the task
For a bill comparison, use the energy you actually paid for and the applicable tariff. For a driving comparison, keep the vehicle’s measurement definition consistent. Keep remaining differences as open questions in the log, with the available records attached.
Match the accounting period first
Imagine an invented log that records 60 kWh supplied at charging sessions during one week and 45 kWh displayed for driving. Before interpreting the 15 kWh difference, check whether the battery began and ended the period at comparable stored-energy levels and whether both records cover the same interval.
If the week ends with more stored energy than it began, some supplied energy remains in the car. Other uses and measurement definitions also need to be considered. The arithmetic identifies a difference; the records determine how much of it can be explained.
Keep a reconciliation sheet
Record the start and end dates, charging receipts, trip-display period and any relevant battery-state information. Add the manufacturer’s definition of the display figure. Mark missing information as open so an explanation can be updated when a record becomes available.
DOE/EPA’s explanation describes charging conversion losses and notes variation with the vehicle, charging system, battery state and conditions. It supports considering losses, while the particular log needs its own evidence for the amount.
For ongoing tracking, use consistent boundaries from one period to the next. Retain the original readings rather than replacing them with a calculated estimate. This lets later comparisons distinguish the recorded figures from the explanation developed around them.
Three labels are useful in an energy log: measured, calculated and still to check. They keep the recorded figures and the working explanation visible together. A later receipt, manual definition or session record can then be added without losing the original observation.
Sources consulted
- Where the Energy Goes: Electric Cars — U.S. Department of Energy and U.S. EPA; checked 4 November 2026.