When we tested the LHB-1000 headlamp, the various batteries we used made a HUGE difference in the how long the headlamp ran and made some difference in how bright it was.
The bottom line was this: Choose the best battery you can buy. Disposable or rechargeable… buy the best. It most definitely makes a difference.
One consideration when buying batteries is whether you should buy disposable or rechargeable. Do rechargeable batteries save you money in the long run? Kim Komando (The Digital Goddess) posted a wonderful article today addressing that exact question. It is well worth the read and should answer the question for you.