Starter battery warning light

This warning light does not work properly. It should stay on after READY illuminates in case the 12 V starter battery has not enough voltage, but that never happens. A technician with more than 10 year MiEV experiece told me that he never saw this warning light staying on.

When the car is in READY, then the HV pack is connected to the Motor Control Unit and the DC Converter.

The DCC creates 14.4 VDC from the HV and sends it directly to the starter battery positive terminal to charge the starter and keep it full; so even if the starter is old and weak and too low, then the contribution from the DCC will mask this condition. And as you said the warning light may never happen in READY mode even though it should for a weak starter condition.

An old weak or worn out starter battery can cause a multitude of electrical fault codes in an EV.