Sorry, I meant the positive battery connector post that presses on the positive end of the battery inside the battery tube.
In that case the concept is still somewhat the same...
If you say that the PV has the spring loaded pin, then that just means that the pin in the center of the 501 threading for example has some give to it so if you would put a
tank like the vivi it squashes the pin in the PV and you thread your
tank as much or as little as you want and it still makes contact. This is useful to have so you can put any other
tank or genesis or whatever and if they a have a shorter positive post your PV compensates and makes the connection.
If you mean inside the tube then again the same concept...
You could use the batteries that the manufactures offers and if you someday buy some in another website or shop and they happen to be 1/4" shorter than the recommended ones (as I've learn that protected vs. unprotected length varies, also brand and such), they should still work because again the spring touch so it makes contact.
Again hope that come through as clear as I think it.