Let me clear up a myth about alkaline vs. rechargeables: the voltage may be 1.5v in alkalines, but it drops as the battery drains, to as low as 1.0v. A NiCd or NIMH rechargeable holds a 1.2v charge steady for almost its entire runtime. Some people have been using rechargeables in their controllers for a long time.
As a side note, my Game Boy Advance cautions users to only use alkalines, but who listens to that? I think it's a conspiracy between handheld device manufacturers and alkaline battery manufacturers.
Go for it and save yourself some xtra $