Hi, my iPhone turns off about 100. What is the reason?

iPhone 6 Plus is >7 years old (September 19, 2014) , which also affects the battery life.

Having the battery replaced by Apple or an Apple Authorized Service Providers may resolve the issue.

See here: https://support.apple.com/iphone/repair/service/battery-power

If you are going to replace the battery, by Apple or an Apple Authorized Service Providers read this Apple article:

Get your iPhone, iPad, or iPod touch ready for service

https://support.apple.com/en-us/HT201557

You may get better and prompt responses if you may kindly provide the iPhone Model that you have and the iOS version if it is known to you and re-post.

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