Unclear which exactly you mean, but many of those lights will work on NiMH or NiCd cells, too.

I actually have a little flashlight that takes either an alkaline AA, a rechargeable AA, or a 14500 lithium. As a need-targeted helmet light it's plenty for urban circumstances, not really enough for the MUP out in the wilds but it goes along there anyway as my backup to larger solutions, and as the light I bring "just in case" on "this will be over long before dusk" rides. I generally run it on rechargeables of one sort or another, but a fresh alkaline AA doesn't weigh much to bring as a backup.

If you mean those silicone-strap-encased coin cell rear blinky's, those are also nice as a minimal/unplanned-after-dark solution, though I sometimes mount something more if I'm going to be in actual traffic and not a MUP or lane.