ugrey,
I know nothing, and post useless posts all the time... /ubbthreads/images/graemlins/smile.gif.
Your G2 is plastic and has a lexan (plastic) lens...SF recommends the P61 for that light, but you don't know if the Maxfire uses lower heat tolerant plastics.
http://www.surefire.com/maxexp/main/co_disp/displ/carfnbr/228/prrfnbr/878
According to Brock's tests the P61 is about 8.5w. bwaites uses high-current capable NiMH's in his Maxfire R-mod., so those batteries will not get as hot from the 2.3amp draw of the P61, compared to Lithium primary cells.
http://www.uwgb.edu/nevermab/flash.htm
However, as an emergency light, 20minutes seems an arbitrarly short runtime choice? For a simple drop in replacement this is an easily upgrade...but.
Do you know if the E1 module would fit in as an exact replacement for the Maxfire module (put some cardboard between the battery tail cap contact, to prevent the light from going on, and then see if the E1 module fits securely into the Maxfire? Reason I ask, is if you have any blown out E series modules, it might be possible to do an more adavanced mod., requiring soldering and such, to get you 1hr of runtime for about the same level of higher output light at only 6watts.
That's assuming you don't mind the general beam that the stock Maxfire reflector produces. Since I haven't done the mod yet (on my to do list for next year, as the Maxfire at $20 makes it possible to have 2 of these for the price of one G2), someone else should see if it's possible before I get around to doing that mod. Maybe the 'useful' bwaites can do this, having more free time on his hands than I do at present.
It might be possible to do the same mod to the Maxfire module, but I'm not sure if the plastics in that module can handle the heat, some plastics will melt at 4watts or less. $25 P61 is rather expensive for a $20 Maxfire. I'd rather take the time to solder in $6 bulbs that give me 40+ minutes runtime on Lithium primaries. That way you have bought 2 lights for the price of one G2 +single P61.