theres a groove on the inside of the barrel in which the head contacts when fully tightened down, check for surface aberrations such as wear or impurities, like dried grease.
Also check the two "wings" on the side of the head, they resemble two rectangles poking out of an otherwise round PCB, those areas contact the body when its turned on, check for solder wear or pad damage...if your careful enough you can apply some solder and sand it down to the right height, or the E01 may turn on way before its tightened down
It is very unlikely that the battery tube would have an issue, unles the battery leaked before. It would be more likely to suggest that, through requent use, the contacts on your E01 head somehow [dunno how] spaced its tolerance a little too far. I own and use about 8 E01s and the one occurace that requires me to swap heads is the occiasional snugness of o-rings in certain bodies and looseness in others:whistle:
