Charging has finished and the wallbox shows 20 kWh, yet the car's display or your estimate suggests less reached the battery. Which figure should be used for charging cost, and which shows the energy available for the next journey?
Both describe the same charge but measure different things. Once that is clear, you know which figures are comparable and what to investigate.
Agree the measurement point before settling costs
Suppose 20 kWh passes through the charger meter while a separate measurement says 18 kWh is stored in the battery. The difference is 2 kWh and stored energy is 90 percent of the input.
This is an invented example, not a product test or general loss ratio. Energy measured at the charger and energy stored in the battery are different quantities.
If an agreement uses charger-metered energy and the illustrative unit price is 60 Ft/kWh, the energy value is 20 × 60 = 1200 Ft. Using 18 kWh gives 1080 Ft from another measurement point. The 120 Ft difference does not decide which is correct; the agreement must define that in advance.
What happens along the energy path?
During alternating-current (AC) home charging, the car's onboard charger converts AC into the direct current the battery needs. Conversion and vehicle systems operating during charging consume energy; heat can also arise in cables and the battery.
ADAC tested charging and considered conversion and auxiliary loads separately. Its findings apply to the cars and conditions tested. ADAC's charging-loss study presents the measurements.
The difference from one session cannot therefore isolate the wallbox's own loss. Vehicle operation and the measurement boundary also contribute.
The electricity meter can show a third picture
The building meter measures all energy passing through it. If the oven, heating or other appliances run, their consumption may be included in grid imports.
At a solar home, local generation can contribute to charging. The charger may show 20 kWh while less was drawn from the grid. Energy delivered by the charger and its source are separate questions.
| Your question | The relevant data |
|---|---|
| How much energy belongs to this charging session? | The suitable meter reading for the completed session |
| How much energy came from the grid? | Grid measurement for the same period |
| How much did the battery's energy content increase? | Suitable vehicle data or separate measurement |
Use one consistent source for each question rather than substituting figures from different displays.
A percentage is not an energy meter
If the car rises from 40 to 70 percent, multiplying the 30 percentage-point increase by catalogue battery size looks tempting. It remains an estimate: usable capacity and the car's method of calculating percentage would both be needed.
Starting and ending state of charge is useful supporting information in a daily log. For comparable input energy, always use the same suitable meter.
Go 2's integrated meter and display, compliant with the European Measuring Instruments Directive (MID), let you track charging energy. Use the value for the purpose agreed in advance. The manufacturer's Go 2 data sheet details its metering.
Assess standby over a different timescale
The same data sheet specifies 2.5 W standby power. If unchanged for an entire year, theoretical annual consumption is 2.5 × 24 × 365 / 1000 = 21.9 kWh.
That assumes constant standby consumption. A real annual figure requires knowing how long the charger spends in each state. A standby power rating in watts does not describe energy consumed during a charge.
Begin your log with three comparable sessions
For three similar sessions, record start, finish, charger-metered kWh and vehicle state of charge. Note pre-heating and other factors that may affect the comparison. Keep grid and solar data separate.
When investigating a difference, compare the same period and completed sessions. You can then ask a precise question: why did measured energy differ under similar conditions? The log is a sound starting point for understanding your system.
Choose a charger with the measurement you need
On our contact page, give the car model and tell us whether consumption is for your own tracking or a formal report. We can help select the Zaptec model with the required metering.
