Dwc,
The battery slots are pretty well hidden in some masks, even if the work with photo cells function, they still need the batteries to store the energy. Over the years I've had a few, used frequently they sometimes stay charged, others don't! It's not always the "good" ones that last, the one I've been using for a long time was in a bundle with a "Gys" welder!
I'd open it up, nothing to loose!