The guide states you must remove the battery in order to replace the hard drive. This is incorrect- it is merely a safety precaution. If you do not have the specific pentalobe screwdriver, DO NOT ATTEMPT THIS. I just replaced a hard-drive in one of these macs, that someone had already stripped the screw head. The screws are tapered too, so no getting it out once stripped.
The battery does not interfere with this repair, so simply remove the two screws on the hard-drive bracket (step 8), replace the drive then put the mac back together.