Tried other cheaper replacement parts- i fixit is worth the higher price tag
Battery was lasting 5 hours and dying amazingly quick after 1.5 years of use. Downloaded one of those battery life checker apps and it said I was at half or 3/4th life... thought hey I'm getting a new one soon anyway so I'd try it out and have replaced screens and stuff before from ifixit with 90% part working the next year. Soooo I did
Didn't realize they put a seal around the 6s's. I am used to fixing 6's and 5s so taking off the screen was a pain but after 20 min I got it. The battery was also a pain but found a tiny little spatula thing lying around and pulled it off in the driveway due to fearing it might pop and combust... went alright the battery casing kinda bubbled but no fire. Put some electrical tape in to keep it from moving and voila. The battery lasts a lot longer... actually took me like 6 hours to run it to below 10% fell asleep trying to do that so it can get a full charge.
Only advice is buy some electrical double sided tape... it moves a little. If only they made it to fit more snugg instead of apple and everyone giving us these smaller battery's