I expect you would get a period at max brightness and then they would fade.
The internal circuits dictate a lot.. I doubt max brightness would last longer than half hour (if that) but the dimming tends to be quite slow from there on in.
Could be way off, but that's my experience of LED tech thus far..
Even regulated circuits behave the same, my Peli flashlight (high quality, relatively pricey), runs on CR123A's, does..
But AAA batteries are only 99p a dozen at the 99p store
comes with rechargeable pack (consists of 4 batteries wrapped up and a lead). Best light I've ever used. For that price I thought if it lasts a winter I am happy, but it'll be heading into a 2nd winter this year Link here: http://www.dealextreme.com/details.dx/sku.25149