Break off the battery contacts by wiggling gently. A stiff breeze might take them off too.

Using a cutting wheel on a rotary tool (e.g. Dremel), cut the brackets off in multiple steps.

First cut off the long horizontal bar (furthest from the PO). This gives your cutting wheel access closer to the board.

Then cut as close as you can to the surface. Take care not to grind the board itself. You can see I accidentally took a bunch of the enamel off near the bottom left post in the image.

If you're using foam tape, it just needs to be low enough to fit the tape. The gap from foam tape is good because the built in speaker holes are behind the battery. (Seen on the right side)