You can get rid of the traditional 12 VDC battery and use something else. The lower voltage and higher voltage systems have to be present, but there are many ways besides a 12 VDC lead acid to meet the safety requirements for disconnecting the traction battery. The Ioniq uses an additional 12 VDC Li-ion module.If the Ioniq doesn't have that 12 VDC battery, then the HV battery is always live and that is DANGEROUS. Maybe they get around the danger by placing the DC-DC converter directly on the HVDC terminals and the 12 VDC output is always live and fused. Then the HVDC output is through a relay under the 12 VDC power as it is done on other EVs. But it is risky in a way.