My iphone 12 loses power overnight

Hello Glarth,

Thanks for asking the Apple Support Communities about your iPhone battery power. Even with the device powered off, battery power will dissipate over time. So if it's not off, and not charging, you will lose power.

Most people put the phone on charge at night, and then wake up to a 100% device. The new lithium batteries can not overcharge, so this is common practice.

You can check your settings, and see if an app is running in the background at night which is using all the power. Use this help article to check what is using the battery. Any specific apps using your battery more than you expect shown there? You want to check Settings >  Battery the level, activity, Screen On and Screen Off times for the past 24 hours, including the top apps using power? About the battery usage on your iPhone, iPad, and iPod touch - Apple Support

Also check Settings > Battery > Last 24 hours tab > and check Screen On / Screen Off and the top 6 or 8 apps in that list. Does it look like any apps are running more or using more power than you expect to be used? Let us know if some apps look like they are using more power than you are actually using them.

Your battery is designed to retain 80% max capacity at 500 charge cycles, so if an issue is found later, the warranty would cover it as mentioned here: iPhone Battery and Performance - Apple Support

“A normal battery is designed to retain up to 80% of its original capacity at 500 complete charge cycles when operating under normal conditions. The one-year warranty includes service coverage for a defective battery. If it is out of warranty, Apple offers battery service for a charge.”

Battery percentage and charge cycles are both a direct result of use and charging, please check your settings, as some simple changes can really help extend the life of your battery. This same article should help: iPhone Battery and Performance - Apple Support

Follow this for more tips: Batteries - Maximizing Performance - Apple

It may also be beneficial to disable Background App Refresh for the apps that you do not normally use. This article talks about Background App refresh: Switch apps on your iPhone, iPad, or iPod touch - Apple Support

Also, check if your model is capable of this, as it greatly reduces the battery life with active listening. iPhone 14 Pro Max also has the Sound Recognition feature, which uses a lot of battery that was not consistent with other usage. Please check for Sound Recognition feature. Once turned off, battery usage should go back to expected use.

Also, the testing for iPhone batteries are described here: iPhone - Battery Test Information - Apple

Where the settings are all default, any deviation from these settings on your device will reduce the battery life: “All settings were default except: Bluetooth was paired with headphones; Wi-Fi was associated with a network; the Wi-Fi feature Ask to Join Networks, Auto-Brightness, and True Tone were turned off.”

Now that you are adjusting your settings, you may get longer battery charge, and also longer battery life. Thanks.