A simple and low cost solution to mount the battery packs to the board containing charging components is to use Velcro straps. With cuts on the sides of a rectangular retaining box for the strap to loop around, the battery will be in locked position with minimum movement.
This design uses a locking latch along with a hinge to form a door that could be closed and opened. An enclosure underneath the board keeps the battery in place while allowing access from above.
Similar to the design above, the battery pack is housed in an enclosure with an access door. The door is held closed using a push latch. The latch clamps down on the ball mounted onto the door when force is applied. The latch releases ball also with the application of force. This design will give the board a flush look with much of bulk placed behind the board.