I have a bunch of AAA NiMH's, so I started running them in my ARC. I use mine several times a night, as I wear it around my neck & don't normally turn on the lights when I go in another room. The 1st battery finally went to moon mode after 4 weeks. I can't say I notice an output difference from alkalines. If I do a side-by-side, I can, but for normal use, it puts out plenty of light. This is the 1st battery I've ever had in the light where you actually see it flip to moon mode. On alkalines, you just notice after awhile, it's dimmer. With the rechargeable, when it gets low, it comes on full bright for 2 or 3 seconds, then goes to about 1/2 output. Then if you turn it off & back on, it goes to bright & stays bright, as advertised by Peter. I 1st thought it was a bad connection, but it did the same thing consistantly, several times. When it goes to moon mode, the battery was at 1.13V, which shouldn't hurt the NiMH. TX
PS
My batteries are only 550mah.