The Nichia LED's in the A2 are actually overdriven a bit when running standard CR123A primaries. When run on two IMR16340/RCR16340 cells, the LED's get [FONT=Verdana,Arial,Tahoma,Calibri,Geneva,sans-serif]absolutely[/FONT] nuked with overdrive, enough that the lifespan is unquestionably effected.
However, many here on CPF have run their's for years and years with Li-ion 16340's with no issues. The LED's brightness and lifespan surely have been reduced, but it's not something one would notice over a long period of time. YMMV
I faced this situation myself, wanting to run rechargeables, but not wanting to overdrive the factory LED ring too hard. The answer I found was to run two 3.2V K2 Energy Lifepo4 123A cells. They have a legitimate 600mah rating, which is just as good as most 16340 Li-ion's, and have a fully charged resting voltage of around 3.4V, which is slightly more than a CR123, but far less than Li-ion's 4.2V.
I get 30 minutes runtime with them using Tad's 3712 bulb in the A2.