Battery replacement faster and easier than expected/guide
Battery was old and phone wasn't holding a charge.
Repair was much faster and easier than the guide and online posts. Took me 10 minutes with the standard iFixIt repair kit, which had everything needed and more. Now my iPhone battery and speed is back to normal. Great website, videos and guides!
Step 13-16 can be skipped with a well placed prop or another set of helping hands. This limits things that can go wrong. Go super slow and patient on step 8. My screen started separating from plastic bezel. Trick is to use the blue pry tool EVENLY with the suction cup. Read the comments to the repair guide you are using, some where helpful as well.