iPhone 6s battery drains fast
My Battery drains fast
[Re-Titled by Moderator]
iPhone 6s, iOS 15
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iPhone 6S (September 9, 2015) is > 7 years old, which also affects the battery life. The hardware remains old, so does the battery.
Having the battery replaced by Apple or an Apple Authorized Service Providers may resolve the issue, if it is still possible.
The battery can be replaced by Apple or an Apple Authorized Service Provider.
See this Apple article: iPhone Battery Repair & Replacement - Apple Support
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
Get your iPhone, iPad, or iPod touch ready for service - Apple Support