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can I use an iPhone 6 plus battery in an iPhone 6s plus
Edit: You can use the battery from an iPhone 6 Plus in an iPhone 6s Plus, just keep in mind that the iPhone 6 Plus battery is thicker, which may affect the seal you get batween the display and the casing. Source
The batteries have different capacities but you can still use them as the 6plus 6s and 6s plus all use the same connector.
Yes, no dought you can use it. I used it so many times and no issues.