I know I'm a behind, and this will be remedial, but maybe someone will gain something from this. Given the 18V max I thought that maybe I could push it with various battery configs to get it to put out close to the 320 lumens. I mean it is way brighter than the P3 that I had, but it didn't matter the config. 2X AW 18560 3100maF; 1X AW 18650 3100maF, 4 RCR, 2RCR, the output was the same. So I just decided to use these to replace the G2 drop ins and run them on 2 RCR. I'd heard heat was an issue, but that seemed doubtful to me as the output isn't that robust, but I ran it continously for 20 minutes and the head got only slightly warm as was the case with the batteries. Certainly a huge improvement for the G2 and the heat doesn't seem to be a problem, so it seems appropriate for the G2. The drop in fits nicely without the spring and it's beam is nice as it's a good bit more floody. But by contrast to the XML U2 it's comparitavely anemic.
For what it's worth.
For what it's worth.