best choices of batteries ?

Hello
I have recently built my first laser , whipped out my laser diode from a dvd burner , drove it with a LM317 . however, my question is what kind of batterys should i use to get 9 volts ?
I mean , why using 6 AAs where I can use one 9 Volts battery ?
if I used AAs can I use a rechargeable ones ?
consider I am using a high quality AA batteries, how long will they last ?

another quick question I know that this is not the right forum , but how can I determine my diode's power ?
thanks

Regarding 9V batteries - never. They can't supply the current you require from them. Instead, use two li-ion batteries. They are 4.2V at max charge each, and they can supply a crap-ton of current.