thanks for your feedback ! Good point for the o-rings : the holder for the crystal is pretty tight, but you're right, during a duel, things can get loose.
The batteries are just 4 AA, niMH, 2600 mAh. I used the holder + heatshrink kit I'm selling. Making a pack has never been so easy (I used to struggle when I was soldering cell together with copper tape). And it's very convenient in the graflex, since the ID is large compared to the hilts I usually make with a chromed tube (35mm OD / 33.80 mm ID).
What is not really displayed on the picture is the way the whole thing is tied inside the hilt. The central section of the craddle is twice thicker and matches 2 little holes in the lower part of the hilt. Then you shove the battery section + speaker holder in that section and 2 headless screw block the craddle. Since the graflex hilt is thick, the hole is also threaded, so I have two matching threads for each holes, and the cradle won't move at all.