I'm using rechargeables in the regular Infinity and in the Ultra-G. It's cheaper than alkalines, and I use both of my lights for more than an hour a day. The fact that you can use up old AA's doesn't mean anything to me - people who use this approach probably rarely use their lights.
I want a brighter light, and I'm not willing to throw away money on Lithiums when I can use rechargeables. Rayovac 15 minute batteries are just as bright as new alkalines.