I'm not really expecting 900 lumens from it using just 1x 14500 battery of course, but all similar models I've seen use a 4x 18650 pack at 8.4v, and I was wondering if this could be used with a larger battery pack for more light/longevity when needed.
Apparently looks like a nice design, and It should be easy to connect a fake battery as a connector to use an extra pack on your pocket with a bigger battery pack, but use them parallel, I don't think it will handle with 8.4V.
And of course it will be quite far from those 900 lumens.
But this is like playing the lotto, you have to take the risk to know for sure.
I don't really need devastating brightness from this, so I will stick with the 4.2v supply. I presume the extra amperage available from a 4x 18650 supply may increase the power somewhat. I'll be more than happy if it produces even half of the claimed lumens.