Here is the chart for battery charge from the Shorai website:
The voltages given are no-load voltages.
My battery is an 16AH battery. I am wondering if I could have gone form fully charged to below 10% in about 30-40 minutes with a load of the dash, ECU and headlights.
This would mean that 18AH would have been used up, or 32A-24A for that 30-40 minutes.
My headlight is 55W - at 12V that's 4.5A.
I don't think the ECU and dash would draw the remainder of the current.
Hopefully, I am just paranoid. I'll have to wait until morning to see.