Will a KL4 suck li-ion dry?

I recently got a Surefire KL4 head. I love it, but I want to run it on rechargeable li-ion cells. I have a nice TranquillityBase 18650 body tube, and it works great. I'd like to know what experience people have had running the KL4 on li-ion.

I had been using it quite a bit for a couple days, and finally the cell was beginning to run down. The output started dropping, but it almost seemed as if it was dropping in steps. I wasn't expecting that at all. I figured it would gradually dim as the cell ran out.

I pulled the cell, and it measured about 3.18 volts after sitting for a few minutes. Does anyone know how low it would go if I hadn't been there to turn it off?

The L4 will go into moon mode, better recharge the battery.

Use a protected 18650 and you won't have this problem. Alternatively, you could use the protected 18650 to see if it goes into moon mode before cutting out.