Solder,
Very cool project!!! Please let me know when the PCB (fully populated or bare board available - if bare board, can you provide the BOM?).
What enclosure do you have for the board? How does the cable connect to Spark's CAN bus?
I use DCFC on 2015 Spark EV at least 2 times a week. From xx to 80% of SOC, the displayed current on the dashboard shows "HIGH". After the SOC exceed 80%, the display shows "MEDIUM" and at around 95% SOC, the display shows "LOW". Check SOC WITH Onstar MyLink app. EVSE uses ABB setup.
JC