I think NiCad batteries, once failed are typically gone forever. I believe they can reverse polarity if completely discharged or otherwise abused. But they are fairly benign as modern batteries go.
And I don't believe the teflon insulation burns - plastic does, for sure. The teflon insulation needs a decent cutter tool whereas plastic insulation can easily be torn off, sometimes with your pocket knife or even a thumbnail.
I have an old glow starter with a screw off metal base, so you can replace the battery. It's rather bulky.
L.
"My roommate got a pet elephant. Then it got lost. It's in the apartment somewhere." -Steven Wright