Yes, many of us have experienced the same thing, and have also used the double-band idea.
There's a lot of variance in the behavior of the battery endcaps, due to the tolerance stackup of the laser cutting, and the dimensions of the tubes. If your battery endcap seems to come off easily, visually check that the O-ring is making a good seal before going for the first dive, and monitor it closely for the first couple of dives. Sometimes these endcaps that seem loose will seal just fine, other times they will leak.
I just replaced an endcap on one of my ROVs that had the same symptom, and it was leaking. I took off the O-rings on a number of endcaps that I had, and measured the O-ring groove diameters with a micrometer. The one that was loose and was leaking was about 0.2 mm smaller in diameter than the others. Probably the laser cutter was getting out of alignment that day.
For future OROV releases, we are looking at moving to a thicker O-ring on the battery endcaps, much the same as what was done on the main tube in revision 2.6, to get around issues of tolerance stackup.