How do you know the light you rented was more trustworthy than your own?
The "Team" argument is BS because team separation (especially in a 4 man team which is a "crowd") can happen all the time, whether by choice, or by accident, and you could have been left alone in the cave with a dive shop rental light of which you had no idea about the history and state of the battery.
Equally, you had no idea of the reliability of the lights of your buddies (or any other part of their equipment as a matter of fact).
You started the dive with equipment which was critical to YOUR dive and YOUR safety and had no way of knowing its reliability (acceptable maybe in Scuba 101 dives, but certainly not cave diving).
Don't you have some rules in the USMC about knowing your weapons or you just pick-up the first M4 you find lying about (or a rental and go to war...)?
This is my rifle. There are many like it, but this one is mine. My rifle is my best friend. It is my life. I must master it as I must master my life. My rifle, without me, is useless. Without my rifle, I am useless. I must fire my rifle true. I must shoot straighter than my enemy who is trying to kill me. I must shoot him before he shoots me. I will... My rifle and I know that what counts in this war is not the rounds we fire, the noise of our burst, nor the smoke we make. We know that it is the hits that count. We will hit...My rifle is human, even as I, because it is my life. Thus, I will learn it as a brother. I will learn its weaknesses, its strength, its parts, its accessories, its sights and its barrel. I will keep my rifle clean and ready, even as I am clean and ready. We will become part of each other. We will...Before God, I swear this creed. My rifle and I are the defenders of my country. We are the masters of our enemy. We are the saviors of my life. So be it, until victory is America's and there is no enemy.
Rental gear may be fine for Scuba 101 dives because in Scuba 101 dives there are entirely different conditions and risks from those you find instead in a cave.
As to the rest of your comments, my Risk Assessment of that dive that day holds and you cannot fault it nor can anybody else in this respectable forum.
---------- Post added February 3rd, 2014 at 03:04 AM ----------
No.
In cave diving I do not follow rules which are not suitable to the environment or where an alternative rule including of my own making can reduce my risk and this can be reasonably shown in a formal risk assessment.
It is Risk Management and Self-preservation 101.