The older chemistry has to do with performance, not safety.
I’ll try to explain why I think the protected KP 5200 mah is not a good choice for this light.
A boost driver tries to put out a set amount of voltage and amperage to the emitter on Turbo.
On the other side of the driver, it is pulling in roughly half the voltage and roughly double the amperage. I say “roughly” because driver efficiency and some other things come in to play.
As battery voltage drops, the driver has to pull more amperage out of it to compensate. This is Ohms law.
Now the driver has its limitation on how much amperage it can draw to keep from burning itself up. The driver engineers will decide on a safe limit. Once this amperage limit is reached, the light will either step down the the next lowest level or maybe do a half step down. This reduces the amperage being drawn by the driver, keeping it safe.
I don’t have the batteries to test it, but I’m sure that a fully charged protected KP 5200 mah will show a larger amp draw compared to an unprotected blue Liitokala 5000 mah, for instance, due to its voltage sagging a lot under load.
What this means is that you can test these two batteries by running the light on Turbo for 2 minutes, let it cool, run Turbo again for 2 minutes, repeat over and over.
The Liitokala may be able to run full Turbo for a combined 30 minutes (just an example as I haven’t ran this test). While the protected KP 5200 mah may only get 15 minutes.
So the KP 5200 is a perfectly safe battery to use, but you won’t get as much run time on turbo.
I would love to see Maukka or other more professional reviewers graph the output of this light with some different batteries to see how they compare. Other boost driven lights have shown to give more Turbo run time when used with unprotected high drain cells.
EDIT: For more on this boost driver design, see post #49 below.