+1 on the K2 LFPs being super flat on the charge curve. They’re also very robust and can take abusive charge/discharge cycles. A charger that takes them up to 4.2 volts is technically overcharging them, and it’s like they just don’t care.
It might run in regulation, but for a fraction of the runtime.
This is tail current of single mode Fury with different batteries or voltage.
As you see, lower voltage takes higher current as far as regulator can componsate total power (Voltage x Ampere) to LED
When power is within the range, regulation is acceptable and good.