This may or may not apply to VF clones. I'm talking about the authentic here.
When you insert batteries into the slots, be careful to insert them nice and straight, without letting the thread crests bite into the wrapper. If you don't, some of the plastic may get shaved off the wrapper and end up at the bottom of the thread. Then when you screw the bottom plug back in, it may seize up hard.
My advice is, when you tighten a plug, push slightly on it (or on the coin) to compensate for the pressure of the + contact, and if you feel *any* uneven resistance, stop and thoroughly clean the threads with a dry toothbrush. When the threads are totally clean, there should not be any "scratchiness" when tightening the plug.
Ironically, this is due to the better quality of the threading: if anything gets in-between the male and female threads, bad things happen. With lower quality threads, the fit is poorer and there's room for a little bit of crud.
When you insert batteries into the slots, be careful to insert them nice and straight, without letting the thread crests bite into the wrapper. If you don't, some of the plastic may get shaved off the wrapper and end up at the bottom of the thread. Then when you screw the bottom plug back in, it may seize up hard.
My advice is, when you tighten a plug, push slightly on it (or on the coin) to compensate for the pressure of the + contact, and if you feel *any* uneven resistance, stop and thoroughly clean the threads with a dry toothbrush. When the threads are totally clean, there should not be any "scratchiness" when tightening the plug.
Ironically, this is due to the better quality of the threading: if anything gets in-between the male and female threads, bad things happen. With lower quality threads, the fit is poorer and there's room for a little bit of crud.