Irregular battery experience

[ZT-2874a36c]

Please tell us some basic information before asking for help:
Model Name:asus 6z
Firmware Version:18.0610.2104.145
Rooted or not: not
Frequency of Occurrence: 5-6 times a week
APP Name & APP Version (If your issue relates to the app):
In addition to information above, please also provide as much details as you can, e.g., using scenario, what troubleshooting you've already done, screenshot, etc.
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I am a 6z user since 2 years and I really love this device. No performance issues and almost everything is working intact. But since last update I am facing battery issue. I can't perfectly explain the issue here is description:
I normally do all possible things in battery care settings to keep battery performance good. I always use slow charge setting to improve life of battery and have set up battery charge limit to 90%(would have put it to 80% but I am a heavy user) . Sometimes if I need my phone urgently I turn off slow charging. All was going fine until last update. I am facing irregular performance from battery sometimes it lasts for 8-10 hrs and sometimes it lasts for just 5 hours on same type of usage. Also if I turn off slow charging phone starts charging insanely fast(1% every 5 seconds) . I really love this device but such charging glitch puts a fear of device getting damaged. Please help me about this issue as I don't want my phone dead.
[Note:- this problem arrived after last update]
No any other complaints about this device. This is a good piece of engineering. Good work asus and keep doing same.

[fussion_ASUS]

Hi, when you say that your SOT (Screen on Time) has gone down, can you share the SOT after trying the below:
1. Charge the battery to 100% & use as per your normal usage pattern
2. When the battery strength reaches 10%, go to settings = Battery => Tap on the battery icon & share the graph
3. settings => Battery => Check the screen & share the same.

Also, follow the below steps may improve battery backup: 
1. Enable “Power saver” (Settings > Power management)
2. Close apps that are not used (Bluetooth, WiFi, GPS, etc.)
3. Adjust sleep time and brightness (Settings > Display)
4. Boost memory when you see memory consumption is high with no app running,
5. check for background running applications, stop/disable unwanted apps, you can manage apps from auto-start manager.

[ZT-2874a36c]

I know that battery degrades after use for years and I don't have too much concern about that but main problem to be noticed is charging issue. When I disable slow charging phone starts to charge insanely fast(about 1% every 5 sec) which seems really dangerous to phone. Also I don't use (haven't used till date)any other charger other than provided in box to charge my device.

1. Power saver is good setting but only if battery is too low
2. Wifi, bluetooth,gps and such are always turned off until not needed
3. Brightness is maximum times set on lowest except when playing games.
4. Memory boost ok I will try that.
5. Optiflex is always enabled and I close apps when not needed.

[fussion_ASUS]

Hi, we suggest you to please visit the nearest ASUS service center for better assistance. We request you to call the service center before visiting. Locate here: https://www.asus.com/in/support/Service-Center/India