I have a Dewalt 18v battery that came with a tool at an auction.
If I put it partly in my drill it works fine, but putting it in all the way
breakes the connection. Sometimes if I wiggle it around it will work
briefly all the way in.
It works that way in 3 tools, and a new battery works normally; so it is the
battery.

I have put contact cleaner on it, scratched it up with a file, and tried
bending the contacts in an out; but nothing helps. The blades look pretty
much like the ones on the good battery, so I can't imagine why it isn't
making contact. Any suggestions?