I noticed that upon applying the brake, only one (left) tail lamp lit up. Checked the right one and didn’t see any obvious physical damage. Nonetheless, disconnected it and connected a fully charged Lead Acid 12v Battery (12v Li-ion battery remained connected though no activity). Between all the startup sounds, amazingly heard the HV contactors close.

I was able to start charging. The Air conditioner kicked in.

The Li-Ion battery isn’t charging though and I am still getting all the alerts and also a VCFRONT_a746 Low voltage battery disconnected – Reconnect low voltage battery.

I measured the voltage between +ve and -ve terminals on the car and it at 13.7v

I will leave it overnight to see if by any chance the High Voltage battery charges the 12v battery.

The Li-Ion connector has 5 terminals (Pin 1 is +ve, Pin 2 is -ve, Pins 3 & 4 seems to be an interlock loop that terminates on the connecter itself – Green tab with two contacts when checked with a multimeter has continuity and Pin 5 connects to a thin green wire going to the car).

Battery voltages between +ve and -ve is 13.6. Between -ve and pin 5 is 11.6, -ve and either 3 & 4 is 0.

The Li-ion battery likely has a memory or something. After pin 5 drops below 12v, the car doesn’t make any effort to draw power from it. I charged the original Li-Ion battery that came with the car. Voltages between +ve and -ve is 14.5. Between -ve and pin 5 is 12.6. Connected it but the car remains lifeless.