Yesterday I welded some bits up but found my auto welding helmet batteries were dead. Guess how I found out.that left some blind spots for a while. So it's always the case that you have to do some other job rather than the one you want too.
The batteries are spot welded in with flat sheet so I could replace exactly the same but soldering seemed to work fine but the case gaped a bit as the wires are thicker than the sheet metal previously used but it all worked.

Yeah I hold up my mask to the sky and test it dims when the buttons pressed before putting it on if it's been sitting a while. You'll be fine though as the mask still filters out the UV.

My auto darkening helmet defaults to 'dark', it needs batteries to go clear. I quite like it being that way round.