I tried several different batteries, protected and not, buttoned and flat. I tested each battery in another light.

The retaining ring in the tailcap is solid. I don't have a tool which will extend the length of the battery tube to reach the forward retaining ring. There is no play at the MCPCB from the forward side of the battery tube.

I did the wire scrap across the negative battery post and the body. No joy, no LED light.. I didn't think of applying power directly to the LED connections. I'll try that tomorrow. I assume polarity matters.