NiMH batteries are 1.2v, but they have a much flatter discharge curve than alkalines. Alkalines start at 1.5v and quickly decrease from there.Yeah, I replaced the incandescent with an LED. I am still debating on the rechargeable batteries. I haven't looked into the above adapters, but have looked at rechargeable D batteries. I know the problem with *them* are that they are only 1.2 volts each as opposed to the alkaline's 1.5 volts. They would still work, but I might not get as good performance out of them.
I'm either going to use an 18650 and print an adapter, or use some 3-AA to D cell adapters I have with rechargeables on mine. I also have a nice LED module coming. I think I'll opt to leave the rubber button in place, though I agree that it looks gone in the show.