Okay so let’s go over this. The iPhone 6p, 6s, 6sp all use the same connection. I can speak from personal experience that the 7 battery will work just fine in the 6s so that means that the iPhone 7 battery works in the iPhones that work with the 6p batteries. (Aside from cable size) the OP is asking if the 7p battery will fit in the 6p. For that I have tried clipping the 7p battery into the 6sp since I use those batteries for testing when microsoldering if my cable set is being used elsewhere. That being said I tried it one time so have Just been a dummy as the 7 and 7p FPC connection is the same. To add to this just because I have had a positive experience with using a 7 battery in my 6s does not mean that the contacts for the data lines are the same. It also does not mean that it will not cause damage to Tigris or Tristar. I would advise you to use the respective battery for your device. Also if you really want to then you can use the 6sp battery in your 6p. That is fine to do. In the end it’s a battery as long as you don’t have a polarity issue then you’re fine in theory. With battery explosions happening from time to time I don’t want to stick my neck out and say oh yeah sure bro go for it.