Awfully nice of you to share this information, John; however it appears the OP hasn't been here since his last post nearly 2 months ago. My guess is your solution would have been his solution too.

I've never heard of a bike light configured as you describe (with a secondary button cell). Seems unnecessarily complicated for what I assume is a mode memory circuit. I bet Blackburn got a lot of returned headlights that simply needed a $4 button cell.