Cree q5 direct drive circuit help

So I have a 5 mode cree flashlight that I want to just make a one mode high output flashlight. I'm going to run it off of 2 cr123a 3v batteries. I've done some research and I still can't find the maximum voltage I can run through the bulb and what resistor to use, can anyone help me. Thanks

You've done some research? Q5 is a flux bin, not an led, so you need to find out what led you have. This thread might help you visually determine the LED.

If it's an XRE, the XRE data sheet says the maximum recommended current is 1 Amp which it will achieve at 3.7V typical. This is at 25c junction temp so the actual voltage necessary to hit 1 Amp should be several tenths lower, because as led's get hot their resistance drops and the current rises. Here is a calculator where you can enter values and get a recommendation for a resistor: http://led.linear1.org/1led.wiz

I bet that direct-drive on 1xCR123 is quite bright. Using two will burn it out, and using a resistor will not be very efficient. You'll need to use a driver circuit, which thankfully come with (or without) their own modes. If you are determined not to use a driver, then only use 1 CR123 at most.

Right, a single CR123 direct drive will be efficient, but two with resistors wont be because there is such a large voltage differential between the batteries and the led. If you wire the two CR123's in parallel though, you can direct drive without a resistor most likely and get satisfactory output. If you want to use two CR123's in series go with a single mode constant current driver which can be had for only a few dollars.