I never trusted velcro, that's why I'm using a hard attachment.
First, the battery box is made (balsa+glass), together with F1 and F2 (ply):
This is epoxied between the fuse sides (upside down on the board). Now it's a double walled box, giving the nose structure extra torsional rigidity:
Note the tiny bracket (brass, tapped M3 hole) it function will be explained later...
On the level of the box floor, F2 gets a 2 x 25 mm aperture.
This will receive the protruding end of the battery mounting plate (2mm ply)
The battery slides in the box, until the end of the plate locks in F2,
then a tiny M3 bolt is screwed at the other end, locking the plate in place.
The battery is taped with glas reinforced tape to the mounting plate.
It's going nowhere, except with the model.