can I get an iPhone battery replaced for free under my warranty?

Only if an Apple Technician determines that it is a manufacturing defect and not normal "wear and tear." I suggest that you make a Genius Bar appointment at your local Apple Store or Apple Authorized Service Provider to have them take a look and provide you with your options.

kalli292 Said:

"battery: can i get a battery in my phone replaced for free under my warranty?"

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Ask Apple Support:

If deemed a faulty device, and nothing of accidental damage, then the might replace it free of charged. But, that is Apple's call. These are user-to-user forums, meaning no one here has any say in Apple's call in there being a fee or not. Visit this site: iPhone Battery & Power Repair - Apple Support. As it reads: "If your iPhone is covered by warranty, AppleCare+, or consumer law, we'll replace your battery at no charge."

Apple Support Contact Info:

• Contact Us - Choose Locations
• U.S.A. (800)MY-APPLE
• Proceed from there as necessary

Note: Phone calls are taking a bit to go through at the moment, due to lots of calls. With the Coronavirus Pandemic, many are at home at the moment, with much time on their hands to contact Apple. So, just stay on the line, and you will get through :)