Replacement Battery (there are other sources):
https://eustore.ifixit.com/en/Parts/MacBook-Parts/MacBook-Pro-13-Unibody-Mid-2009-Mid-2010-Early-2011-Late-2011-Mid-2012-Battery-New.html
Screws:
Tri-wing screw heads need an (easily available) driver.
General tips for anyone:
The screws are tiny, so always use the correct screw drivers; work on a towel so that the tiny screws don't roll off the table; don't work over bare boards! Use an egg box to put the screws in as you extract them and number the order for reassembly.