The Shorai is not your problem; electric draw and charge is. What is the wattage of the spanky new headlight in low, high, and fully on?
Without looking back through your thread, remind us what the voltage at the battery is at idle, 3k, 4k and 5k please? And repeat that test with the headlight unplugged.
But do this after your battery is fully charged and rested, and reading 13.2v or better. If you keep discharging fully the Shorai, you will damage it.