It's normal for an iPhone battery to drop to 90% in the first 12 months of usage. A drop to 89% in 8 months is slightly abnormal but could make sense. I don't think you have a faulty battery but you should follow the following tips to prevent it from dropping fast. Makes sure you don't level your phone in extreme hot or cold environments.

Last Charged: Indicates how fully the battery was last charged and the time it was disconnected. Battery Level graph (in Last 24 Hours): Shows the battery level, charging intervals, and periods when iPhone was in Low Power Mode or the battery was critically low. Battery Usage graph (in Last 10 Days): Shows the percentage of battery used each day.

Power and Battery 8. Lasts about the same as iPhone 7. Talk time (wireless): Up to 14 hours; Internet use: Up to 12 hours; iPhone 8 and iPhone 8 Plus are splash

Open the “Settings” app and go to “Battery”. Scroll down all the way to the bottom of the Battery Usage section to “Time Since Last Charge” to see the exact amount of time iPhone battery is lasting, broken into two sections. Usage: shows how much actual use the iPhone has had on battery power, since the last time it was fully charged.

This uses a lot of energy. Switch off Wifi & Bluetooth while in Roaming or Not in Range. Enable "Wifi Assist" : Settings > Cellular or Settings > Mobile Data > Wi-Fi Assist [Enable] Periodically Check the Battery Health (Settings > Battery > Battery Health) ( 1) of 1. iPhone 8 battery drain in a few hours. If you’re interested in the actual numbers, we’ve detailed the rumored battery capacities of each iPhone 15 model below: iPhone 15: 3,877mAh (vs 3,279mAh on iPhone 14) iPhone 15 Plus: 4,912mAh . 371 36 167 220 255 159 316 127 390

how long does iphone 8 plus battery last