Saprefm1....From my limited experience with adapters and modding, you will not be able to get the post to stay in without putting the o-ring (gromment?) in first.
Take the o-ring off. Take a close look at it(with a magnifying glass). If it is torn in anyway,it is junk. torn rings cause shorts,shorts are death to a battery. FYI that ring looks like the ring in a 510 carto. Do you have any old ones?
Now the hard part, putting the ring in hole,(take the nova all apart),take a icepick and and puch down on the ring. While holding it down, fold it over with small tweezers, seat in the hole. This is not easy!!!!, sometimes you can do this with a small screwdriver,etc,
and poke it in. It seats half on one side, half on other side of the seat.
Put drop of
juice on the pin,and gentility push it in. Check with a muti-meter? Short are death to battery.
Hope this helps. Good advice to have extras.
Oh and welcome to the forum