The battery percentage on an EV dashboard is an estimate, rather than a direct measurement of energy left in the pack. One input is coulomb counting. The controller measures current flowing into and out of the battery and adds those measurements over time to track charge movement.
Why the current measurement matters
A small measurement offset can accumulate during a long operating period. The battery-management system therefore needs an appropriate starting estimate and other information to keep its calculation useful. Voltage, temperature and the battery model can contribute; the exact method belongs to the vehicle manufacturer.
For a workshop enquiry, describe the behaviour of the percentage display. Does it fall smoothly, jump after parking, change after charging or disagree with another report? Record the starting charge, journey length and conditions. A screenshot with a timestamp is more useful than a recollection that the range seems wrong.
Establish whether energy is missing or the estimate has changed
Ask for the charge estimate to be considered alongside actual use and diagnostic findings. A change in displayed percentage alone cannot establish failed cells or a defective current sensor.
Avoid repeated deep discharge experiments to force the display to relearn. Follow the charging guidance for the specific battery fitted to the car and arrange assessment if the change is sudden or accompanied by a warning.
Arrange an assessment
For EV and hybrid diagnostics, send the vehicle details and fault report to AXION. We support enquiries from drivers and garages. Workshop, postal and remote options depend on the job and are confirmed before booking.
Technical reference
Read the supporting technical documentation. The referenced design or vehicle application defines its scope; it is not a universal repair procedure.
Related reading
Why LFP battery voltage does not give a simple charge percentage. Browse the automotive electronics repair library for other systems and symptoms.