Alkaline Problems

I recently built a 1W+ blue laser. The diode I used is an Osram Pltb450b. My driver ideally outputs 1.25 amps, but I have run into a problem: the amperage dropping. I am using 6 AA batteries in series, and the amperage significantly drops after a total of 20 minutes of use (not one session). What alternatives could I use? (I am also okay with using a wall adapter.)

You can't use li-ion batteries?

That is certainly an option; although I am not sure what li-ion batteries to use.

AA size @ 3.7v per cell nominal 4.2v fully charged
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