12V auxiliary battery drain
ModerateElectrics & ElectronicsThe small 12V battery that powers ancillary systems can drain within days of inactivity, leaving the car completely dead despite a full main battery. The standby draw depletes the 44Ah battery quickly, and repeated deep discharges shorten its lifespan. A BMS software update (TSB 24-01-090H) addresses the worst drains, but some owners still carry a jump pack.
Most affected: All Kona Electric models
Estimated cost: £90–£250Affects: 2018–2023Often appears around: Any; most common after 2 years
Typical symptoms
- •Car completely unresponsive after 2-3 days parked
- •Dashboard warning: "Battery discharge warning"
- •Need to jump-start despite full HV battery
What to inspect before you buy
- ✓Age and health of the 12V battery
- ✓Whether BMS software update has been applied
- ✓Evidence of repeated 12V replacements indicating parasitic draw