Regarding the question in the OP I can’t offer a solution.

What I can offer is a warning, to those who have missed reading this thread.
What we see here is the risk of using a proprietary battery, and no replacement when you need one.
Thus making the light practically useless. Unless you are an experienced modder.

It’s like driving a really nice car that has a unique set of wheels/tyres … and no spare in the boot.
And by the time you need a new set of tyres you find out they don’t make them like that no more.