Mine is a like the one below it's not an original
Then you need to adjust the smaller screw to make contact with the top of the battery.
There's a reason why flashlight tubes and regular regulated tube mods come with a spring at the bottom
When you go for a bottom switch mech, it's a tradeoff with that spring; now you got no spring to make up for small millimeter differences between batteries; one solution is to use a telescopic mech; otherwise, you got to do some sort of adjustments with screws to make contact with the battery.
Your battery shouldn't be rattling/knocking around inside the tube otherwise you have poor electrical contact.