iPhone 15 battery health decline in cold weather

Under average conditions, you can expect your iPhone battery health to decline at a rate of about 1% for every 40-50 charge cycles. In extreme conditions outside of your iPhone’s operating temperature range, such as very cold conditions, your battery health will likely degrade faster. This is because extreme temperature conditions can cause your device to change its behavior to regulate its temperature.

According to Apple, you should use your iPhone between 32º to 95º F for optimal usage.

The iPhone 15 battery should decline at a rate closer to 1% for every 40-50 charge cycles, according to Apple's product information.

Revised, thank you for noting that.