I have had my auto darkening helmet in storage for 9 months and when I took it out to check it, guess what, sometimes it would darken and then another time it wouldn't Should I lay it out in the sun for a day and see if it gets it's memory back?
I am sure that the battery went dead and opened it up to see.
Sure enough there is what looks like a 3 volt lithium cell in there but that is as far as I have gone.
Need to replace the battery for furthur testing, but no rush as I 'happened' onto another one at a giveaway price.
The new one I now hang near the window to keep it charged, if indeed there is a charging circuit built in. There seems to be a mini solar pannel in the lens.
What brand welding mask? There are a lot of brands out there that use the solar power to recharge the battery. Leave it in the light but a new battery is pretty cheap and probally in your future.