Insert an uncut plastic card between the top edge of the battery and the frame.

Insert a second plastic card between the right edge of the battery and the frame.

Don't use excessive force or pry at the battery with metal tools.

Try your best not to deform the battery during this process. Soft-shell lithium-polymer batteries can leak dangerous chemicals, catch fire, or even explode if damaged.

The battery most likely won't budge at this step, but these cards will be helpful as leverage as you continue.