While I've never got steel wool to work with a battery, with a ferro rod it goes up quite nice. For that reason, I have some in my larger kits. However, I noticed that one of my batches must have been in a less that perfect pill bottle- it is rusted.

So, my first thought is to replace it, and the bottle. Then I'm thinking, rust... And remind myself that I'm not Blast, no thermite.

Final thought though is, how about working some petroleum jelly into it for storage. Should keep any moisture at bay.

And maybe I'll mix in something like some magnesium or aluminum flake.