How do I calculate runtime for TerraLUX TLE-300M using 4 D alkalines?

[Photongun]

I'm sure there's a plethora of you out there, but can someone please walk me though how one calculates (equation wise) the expected runtime of a TerraLUX TLE-300M using 4 plain old alkalines. Also is it possible for me to use 4 D 12000mah nimh's with theTLE-300Mor will the voltage be too low?

Assistance would be greatly appreciated.

 

[Marduke]

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http://www.candlepowerforums.com/vb/showthread.php?t=201059