nightgaunt,
Let me put it this way: my SF D2 came with two SF123 lithium batteries already installed. Also, my Arc LS came with the 123 installed as well. No worries.
However, on a related note, here's something I do wonder/worry about: suppose during the hot humid summer you load up your Arc LS with a fresh battery and throw it in the glove box of your car. Wow. Great you are pre-pared! But wait! When you next go to use it, it is late fall or early winter and all of that moisture in the air in the light has condensed out, right? Wouldn't it condense out onto and into the electronics? Has anyone ever had this problem? Is it a problem? It's got to be, right? Where else can the moisture go? The light is waterproof to 50 meters.
Anyone have any thoughts on this? I suppose you could store the light disassembled, or open it periodically during the change of seasons. Perhaps you could throw a few silica gel balls inside? I wouldn't want to do this, personally, but would it work?