For tracking your own charging, the reading is trustworthy — but it is not the same number your car reports, and it is not automatically a figure you can bill someone from. A charger counts the energy that passes through it; the car reports the energy that arrived in its battery. The gap is conversion loss between the two measuring points, not an error.
Key Takeaways
- The charger and the car measure at different points; the car’s lower figure reflects conversion loss, not a fault.
- Home session metering is indicative — consistent enough for records, rarely published with a certified accuracy class.
- Billing from a reading is a separate, regulated job needing an approved meter for the exact model.
Two Readings, Two Measuring Points
An AC charger measures energy on its side of the cable. The car measures, or estimates, what its battery stored. Between those points sits the car’s onboard charger, which converts AC to DC and turns part of the energy into heat. So the car’s figure normally comes out lower, and both can be correct at once.
| Reading | Where it is measured | What it is good for |
|---|---|---|
| Charger display or app | Inside the charger, supply side of the cable | Your own records, session costs, spotting change |
| Car dashboard or app | At the battery, after conversion | Range and battery questions |
| Utility or home meter | Everything the building drew | Whole-bill checks; see our guide to smart meters for EV chargers |
What “Accurate” Means on a Home Charger
Session metering on a home or workplace charger is built to run the session and inform the driver. It is normally consistent from session to session, which is what record-keeping needs: if your overnight charge usually takes a known number of kilowatt-hours for the same miles, a change in the figure tells you something changed. What most home chargers do not publish is a certified accuracy class for the meter inside. If a model states one, it is in the datasheet — that document, not a brochure adjective, is where to check.
For scale: at the U.S. average residential price of 18.31 cents per kWh, a 40 kWh session costs about $7.32 on the charger’s figure. Costing from the car-side figure would understate what you paid — you are billed for what left the wall.
When the Reading Has to Carry Money
Billing a tenant, an employee or a public driver is a different job from informing one. Many markets run evaluated metering regimes for exactly this: in the United States, programmes such as California’s type evaluation and the NIST Handbook 44 framework treat a charger that sells energy by the kilowatt-hour as a commercial measuring device, and Europe uses its own approvals. A number on a screen, however consistent, does not by itself qualify.
The practical rule: if a reading will ever be billed, the meter’s approval for the exact model is a written-confirmation item before purchase — the same discipline our guide to EV charger certifications applies to any mark.
A Rough Sanity Check You Can Do
You cannot calibrate a charger at home, but you can catch a plainly wrong reading:
- Pick a session when little else is running, ideally overnight.
- Note the home meter just before you plug in and just after you unplug.
- Compare the difference with the charger’s session figure.
- Expect the meter’s difference to be somewhat higher — it includes conversion loss and background load.
Treat this as a rough check only. If the figures disagree wildly, or the charger’s figure changes character suddenly, report it to the maker — it is not a number to adjust yourself.
EVDANCE Models and Session Energy Figures
The EV-ACS3210E portable charger pairs with an app that provides energy monitoring, and the EV-ACT3204E wallbox uses RFID and app control, so sessions are recorded per user. EVDANCE pages publish no accuracy class and no billing-meter approval for these models, so both are written-confirmation items if their readings will ever be billed. For home tracking and cost records, their session figures do the job they are designed for.
Frequently Asked Questions
Why does my car show fewer kWh than the charger?
Because the two devices measure at different points. The charger counts energy before the car’s onboard charger converts it; conversion loses some as heat, so the battery-side figure is lower. A gap is expected — one that suddenly grows is worth reporting.
Can I bill a tenant from the figure in the app?
Only if the meter behind that figure is approved for billing in your market and the records meet local rules. An app display alone proves nothing. Confirm the meter and its approval in writing first.
Which number should I use for cost tracking?
The charger’s. Your bill is based on energy drawn from the supply, which is what the charger measures. Use the car-side figure for range questions instead.
Related Reading
- Do You Need a Smart Meter for an EV Charger?
- How Many kWh Does It Take to Charge an EV?
- EV Charger Certifications Explained: CE, UKCA, UL, ETL, CB and What Buyers Should Ask For
