Knock-down the rough spots with a bit of sandpaper...
Here's a little trick with Super Glue - don't blow or rub-off the plastic dust. When you add Super Glue, and press the two dusty parts together it helps fill gaps and improves adhesion.
Load-up the sides of the battery connector with glue... and quickly press it into place.
Make sure that the battery connector is flush with the bottom of the torch base. Else, the clip might have a tendancy to pop-off.
Make everything permanent by adding a little E6000 to the top of the battery connector and around the sides.
Good coverage will partially seal the connector from moisture...
Press the PCB into place.
And, add the base cap - it acts as a spacer to prevent the battery terminals from coming onto contact with the LEDS.
Put a smidge of E6000 on the sides of the container to hold the diffuser in place.
Make sure that the end with the rounded lip is left open - this is the end that the diffuser cap snaps-into.
The battery will fit inside either way... snazzy!
When you're ready to use it, take the battery out and snap it into the base.
Given the capacity of most 9 volt alkaline batteries, I would expect this to light-the-way for several dozen hours.