Primaries just don't cut it for me. Initially they're fine, but if you want want full power, you always have to swap them out for fresh cells, and then you're stuck with a box of depleted cells. If I had M31 LLL/L as a vampire light( or a 3v version of the aa/aaa volt vampire lights made by datiled), then I could use the old cells, otherwise it's a waste and not very environmentally friendly. It's good to remember that improperly disposed of batteries can be extremely toxic and will cause problems long after this forum is gone.