"Remove three 3.1 mm Phillips screws securing the battery near the edge of the upper case".

Using the tools I bought from iFixit, I have got this far, no worries :)

The channels underneath/around these screws appear damaged and will not allow the screw to unwind and come out, therefore, the screws are "stuck". (This is by no means an indictment of the mini screwdrivers.) Any suggestions to help, because the replacement battery will not fit with these screws in place. Thanks.