You have until Dec 31 to replace your iPhone battery for free (w/ warranty or care) or $29 for All

https://support.apple.com/iphone/…tery-power
If you own an iPhone 6 or later that isn’t holding its charge, now is the time to get your battery replaced, you have until December 31 to take advantage of this Free (w/ warranty or AppleCare) or low price $29 to replace your battery.