Yes, but I need to explain myself a bit.
In a single cell light, a boost driver will pull more current as the voltage drops farther and farther from the emitter’s foward voltage to keep it in regulation.
That means using steel springs not bypassed at say 6A current, the voltage drop will be around 0,3V. Which is huge.
Say the output power is 18W for a 6V emitter
Our cell at varying voltages and current draw:
18W= 4,20V x 4,28A
18W = 3,9V x 4,50A
18W = 3,60V x 5,00A
As you can see, current draw increases as voltage decreases.
Now, let’s introduce a steel spring(–0,3V for every voltage)
18W = 3,9V x 4,62A
18W = 3,6V x 5,00A
18W = 3,3V x 5,45A
That means you have to pull even more current out of the cell.
Imagine that but at 50W power! You would be pulling at least 12A at 4,2V, and that could go up to 14A at 3,6V, or even 15A at 3,3V! With only a steel spring and no bypass, that would be go much worse. And that is not even counting the internal resistance of the cell, and other resistance in the circuit.
You’d probably get either a low voltage warning almost instantly due to the huge spring resistance, a burned spring, or a huge power loss.
That problem is still there with a FET driver, but since current pulled goes down with voltage, it isn’t as much trouble.
TLDR: For such a powerful boost driver, going with a single 18650 is crucial for both energy and power density. You also need to get rid of all almost all contact resistance, which includes the springs.
Edit: Remove something I should not have said :person_facepalming: