Tips for alignment:
1. Do not remove the plastic covering the adhesive and then try to align the battery. Leave the plastic on and remove one at a time after the battery is aligned.
2. Use masking tape to hold the battery cells together while aligning, otherwise they flop around a lot.
3. Put your speakers next to the battery cells (before removing plastic on adhesive) to ensure you’re leaving enough room.
4. Make sure your battery connector is well aligned too.
Take a look at the trackpad replacement guide to get a sense of where the adhesive is:
MacBook Pro 13" Retina Display Early 2015のトラックパッドの交換
I also forgot to flip the ZIF connector. Thankfully my trackpad worked after.
Make sure to flip the ZIF connector before putting the trackpad cable back, too.
Tip: Use post-it notes to keep track of screws
1. Pack of post it notes
2. Stick screws to the sticky part of the post it note
3. Write on the post it note which step and what kind of screw it is