Miracle,
I have the Fenix P1D CE. I ran it on Two 3.6V 900mAh RCR123
Rechargeable Batteries. Its runs fine. It is about 25% brighter also
I believe. The threads on this site will tell you for sure.
Your modes won't work correctly with 3.6V.
Low mode will be the same is Med.
Med and high will be about the same.
As the voltage of the 3.6V drops, things will change a bit.
Again the threads on this site will explain it very well.
Now if you run them on two 3.0V RCR123
Rechargeable Batteries all modes will work correctly!
I use these now instead of 3.6V because I want
all my modes to work.
Do a CPF search for Fenix P1D CE.
There is a TON of good info about this light and
running them on 3.0V, 3.6V, 3.7V Rechargeable Batteries.
Here are two threads to get you started...
https://www.candlepowerforums.com/threads/146533
https://www.candlepowerforums.com/threads/147585&page=2&pp=10