The Harbor Freight autodarkening welding helmet with the solar cell
actually has two coin cell batteries inside, and when they get weak,
the autodarkening ceases to function Some times this happens in a
little over a year.

A fellow student in my evening welding class took his apart and
documented the repair in the following web page:

http://www.pskl.us/wp/?p=648

I've also printed this page as a pdf file and uploaded it to the
metalworking dropbox since that's a longer term storage site and the
instructions will be around two years from now when somebody needs
them.

RWL