Why my battery health drop faster?
I just bought Iphone X 4 months ago but my battery health drop to 86%. It is normal or not?
发售于2017年11月3日。型号为 A1865, A1901。有 GSM 或者 CDMA 网络制式可选。提供64或者256GB 的存储空间。提供银色和深空灰色。（读音与“iPhone 10”相同）
"Health" is a measure of discharge rate. The phone has logic that calculates the remaining capacity and compares it to the battery spec. There are apps, sometimes built-in, that will discharge a battery when nothing else is happening for a short time, calculate the discharge rate from the voltage drop, and interpret that as "health".
Every time you discharge a Li-Ion battery to below 10% of spec capacity or charge it to above 95% spec capacity it is damaged slightly, loses capacity slightly faster than normal. The charger furnished with a phone works with the phone to prevent over (+95%) charging, an aftermarket charger may not.
Degradation may seem to be excessive during the early part of a battery's life. Li-Ion batteries have a learning curve and increase capacity during the first series of charging cycles. That's why EVERY device that uses them says to FULLY charge them BEFORE first use. Few users do this.
(I tested a Li-Ion battery pack with a new drill after an initial timed, not indicated, full charge, and timed how long the drill would work, bu drilling holes in wood. I repeated this 5 times. Each time the run time increased. The "capacity" after 5 charges was 20% more than the first time.
For you, more important than absolute "health" is whether its "health" continues to degrade faster than 0.75% per month. A typical Li-Ion phone battery will provide 70% capacity after 3 years of being in continuous service.