OnePlus, like most other Android device makers, doesn't offer removable batteries on their smartphones. On a journey to make its smartphones slim as well as dust and water resistant, OnePlus made it really hard for a novice to swap out an older degraded battery for a new one without paying a visit to a service center. However, the company does have a really handy diagnostic app that can give users a clear insight into the health of their battery.
The app is called "OnePlus Diagnostic" with the package name com.oneplus.healthcheck, which comes as no surprise. Community members of XDA have been aware of this app for quite a long time as OnePlus itself published it on their Chinese support site. The app is compatible with both HydrogenOS and OxygenOS, and you can easily take a look at important battery parameters (e.g. capacity, temperature, charging state, etc.) through its clean and clutter-free UI. The screenshots attached below are from XDA Senior Member Some_Random_Username's OnePlus 5T which he purchased in December of 2017. The OnePlus 5T supports 20W Dash Charging.
The value of the "Battery state" parameter is particularly appealing because it shows the battery wear level. Upon inspecting the app's code, we discovered that the app reads the value from /sys/class/power_supply/bms/battery_health. Here "bms" stands for Battery Management System, while this value is reported by a battery fuel gauge IC made by Maxim Integrated. If that value is < 80, the app reports the battery as having a "serious loss" in capacity.
Some OnePlus devices such as the OnePlus 8 and 8 Pro do not report the battery health at the aforementioned path of the sysfs virtual filesystem, so this app will fail to read it and display "no data". This app won't work if you aren't running OxygenOS (or HydrogenOS) because it requires special privileges to be able to read /sys/class/power_supply/bms/battery_health. If you have a rooted phone, though, you can manually check that value by running the following command in a rooted shell or any terminal emulator app running in elevated mode:
cat /sys/class/power_supply/bms/battery_health
It is worth noting that this diagnostic app is different from the hidden suite of hardware diagnostic tests, also known as "Engineer Mode". In case you want to give OnePlus Diagnostic a try to find out about the battery health of your phone, download the APK from the following link:
Download OnePlus Diagnostic from APK Mirror
Via: /r/OnePlus